LT Journal of Analog Innovation V22N3

www.l inear.com

October 2012 Volume 22 Number 3

I N T H I S I S S U E

Caption

1A, low noise buck-boost

converter with 1.8V–5.5V

input voltage range 9

surge stopper with ideal

diode protects input and

output 12

digital power system

management with analog

control loop for ±0.5% VOUT

accuracy 17

LED PWM dimming

simplified 34

Real Power Density: 26A µModule Regulator Keeps Cool in Tight SpacesEddie Beville

Each generation of high end processors, FPGAs and ASICs demands more power, but even as power supplies are expected to carry significantly heavier loads, they are given less board space to do so. It is now common for POL (point-of-load) supplies to produce multiple voltage rails at tens of amps to over a hundred amps at low, ≤1V, output voltages, and in less space than the generation before.

Supplies that must support high load currents and fit in

tight spaces are often judged primarily on their power

density, or watts/cm2. Indeed, many of the latest pack-

aged power supplies and discrete solutions proclaim

impressively high power densities—power supply man-

ufacturers seem to be able to squeeze more and more

power from smaller packages. Unfortunately, there is a

big problem lurking behind amazing increases in power

density. That problem is heat (see sidebar, page 4).

Heat dissipation is a significant problem at high cur-

rents and low voltages. In many systems, cranking up

the power density actually compounds the problem,

because more power in less space also pumps up the

density of power losses—more heat in less space. It is

not enough to simply squeeze a high power supply onto

a board—the solution must also be carefully evaluated

with regard to power loss and thermal resistance—

two parameters that can make or break an otherwise

good regulator. Claims of high power density can be

(continued on page 4)

The LTM®4620 µModule® regulator enables high current power supplies to fit tight spaces. Thermal management is built into the package to prevent hot spots on the board, a common problem with POL power supplies.

http://www.linear.com

http://www.linear.com/4000

2 | October 2012 : LT Journal of Analog Innovation

In this issue...

Linear in the News

COVER STORY

Real Power Density: 26A µModule Regulator Keeps Cool in Tight SpacesEddie Beville 1

DESIGN FEATURES

Multiple Power Sources No Problem for 1A, Low Noise Buck-Boost Converter with 1.8V–5.5V Input Voltage RangeGenesia Bertelle 9

Surge Stopper with Ideal Diode Protects Input and OutputZhizhong Hou 12

DC/DC Controller Combines Digital Power System Management with Analog Control Loop for ±0.5% VOUT AccuracyHellmuth Witte 17

60V, 4-Switch Synchronous Buck-Boost Controller Regulates Voltage from Wide Ranging Inputs and Charges Batteries at 98.5% Efficiency at 100W+Keith Szolusha 22

100V Micropower No-Opto Isolated Flyback Converter in 5-Lead TSOT-23Min Chen 27

DESIGN IDEAS

What’s New with LTspice IV?Gabino Alonso 30

100V Surge Stopper Protects Components from 300V TransientsHamza Salman Afzal 32

Accurate PWM LED Dimming without External Signal Generators, Clocks or µControllersKeith Szolusha 34

Eliminate Opto-Isolators and Isolated Power Supply from Power over Ethernet Power Sourcing EquipmentHeath Stewart 36

product briefs 38

back page circuits 40

LINEAR ON MARS

The recent groundbreaking mission to Mars, launched by NASA’s Jet Propulsion

Laboratory (JPL), was powered in part by Linear Technology products. Linear’s

high performance analog semiconductors are used in the Mars Science Laboratory

(Curiosity) rover to enable collection of vast amounts of data, including detailed

visual images of the Martian landscape and precise readings to assist scien-

tists in assessing the geology and history of Mars. NASA stated that the goal of

the mission is to help determine whether Mars ever had conditions favorable

for supporting life and whether life could have existed on the red planet.

The Linear Technology devices were selected for the Mars program based on

their performance, precision and reliability, as well as their ability to survive

the harsh environment in flight and on the Martian surface. Linear Technology

products are used in the Mars Curiosity rover and in the spacecraft that deliv-

ered it to Mars. These include power switching regulators to deliver power to

the rover instruments, analog to digital converters for camera motion control

to allow the rover to “see” the Martian landscape and digitize the images for

their long journey back to earth, and operational amplifiers to amplify signals to

precise levels for accurate delivery of data on the composition of the red planet.

“We are proud to continue our 20-year partnership with the NASA Space program

with the current Mars mission,” stated Linear CEO Lothar Maier. “With over

200 Linear Technology devices in the current Mars expedition, we continue to

provide analog products with the highest performance and reliability, whatever

the operating conditions or application. As the breathtaking images and valuable

data come back from Mars, we are honored to contribute to this historic effort.”

In addition to the numerous Linear Technology devices in the current Mars

Curiosity rover, Linear products were part of the Spirit and Opportunity rov-

ers, which landed on Mars in 2004, as well as Mars Global Surveyor, Mars

Pathfinder, Cassini, Deep Space 1, and Mars Odyssey. Linear Technology provides

NASA/JPL with analog integrated circuits that demonstrate the highest perfor-

mance, precision, and reliability in extremely small packages. Linear products

were delivered in radiation hardened versions. Linear’s expertise in high preci-

sion analog circuits provides enabling technology for the sophisticated scientific

instruments and communications systems in the Mars rover and spacecraft.

October 2012 : LT Journal of Analog Innovation | 3

Linear in the news

WIRELESS SENSOR NETWORK PRODUCTS ANNOUNCED

This month Linear is making the first for-

mal announcement of products from the

company’s acquisition of Dust Networks®,

a provider of low power wireless sensor

network (WSN) technology. Dust Networks

pioneered SmartMesh™ networks that

comprise a self-forming mesh of nodes,

or “motes,” which collect and relay data,

and a network manager that monitors

and manages network performance and

sends data to the host application. This

technology is now the basis for a number

of seminal networking standards. The

hallmark of Dust Networks’ technology

is that it combines low power, standards-

based radio technology, time diversity,

frequency diversity and physical diver-

sity—to assure reliability, scalability,

wire-free power source flexibility and

ease-of-use. All motes in a SmartMesh

network—even the routing nodes—are

designed to run on batteries for years,

allowing the ultimate flexibility in placing

sensors exactly where they need to go with

low cost “peel and stick” installations.

Dust Networks’ customers range from

the world’s largest industrial process

automation and control providers such

as GE and Emerson, to innovative, green

companies such as Vigilent and Streetline

Networks. Dust Networks’ technology can

be found in a variety of monitoring and

control solutions, including data center

energy management, renewable energy,

remote monitoring and transportation.

Joy Weiss, President of Linear Technology’s

Dust Networks product group, stated,

“Our primary goal is to enable our

customers to confidently place sensors

anywhere data needs to be gleaned,

cost effectively and requiring minimum

background in wireless networks. The

advent of SmartMesh systems featuring

Eterna™ and the addition of IP-enabled

wireless sensor networks reflect Linear’s

continued commitment to that goal.”

CONFERENCES & EVENTS

Energy Harvesting & Storage Conference, Hyatt

Regency Crystal City at Ronald Reagan Washington

National Airport, Washington, DC, November 7-8,

2012, Booths 4 & 9—Linear will showcase its

Dust Networks wireless sensor network

products as well as energy harvesting

products. Linear’s Joy Weiss will pres-

ent “Low Power WSN Made Practical”

and Jim Noon will speak on the topic,

“Untapped Potential: Energy Harvesting

Solutions.” More info at www.idtechex.

com/energy-harvesting-usa/eh.asp

Electronica 2012, Messe München, Munich, Germany,

November 13-16, 2012, Hall A4, Booth 538—Linear

will exhibit its broad range of analog

products, with particular focus on indus-

trial and automotive applications. More

info at www.electronica.de/en/home

Wireless Congress Systems & Applications,

International Congress Center, Munich, Germany,

November 14–15, 2012—Joy Weiss, President

of Linear’s Dust Networks product

group speaking on “Low Power Wireless

Sensing” in Session 7a, Wireless Sensor

Networks at 11:15 am, November 15.

More info at www.wireless-congress.com

The Battery Show 2012, Suburban Collection

Showplace, Novi, Michigan, November 13-15,

2012, Booth B664—Linear will show its

battery stack monitor and power

management products. Presentation

by Mike Kultgen, “The Key Battery

Management Electronics for Maximum

Pack Performance,” Sapphire/Ruby

Ballroom, 3:30 pm, November 14. More

info at www.thebatteryshow.com n

LINEAR TECHNOLOGY DEVICES PROBE MARSLinear Technology devices used in the Mars Curiosity rover include power switching regulators to deliver power to the rover instruments, ADCs for camera motion control to allow the rovers to “see” the Martian landscape and digitize the images for their long journey back to earth, and operational amplifiers to amplify signals to precise levels for accurate delivery of data on the composition of the red planet.

http://www.idtechex.com/energy-harvesting-usa/eh.asp

http://www.idtechex.com/energy-harvesting-usa/eh.asp

http://www.electronica.de/en/home

http://www.wireless-congress.com/

http://www.thebatteryshow.com/


at maximum load currents, even in

elevated temperature environments.

Figure 1 shows the LTM4620

15mm × 15mm × 4.41mm LGA package.

A single device can deliver two inde-

pendent outputs at 13A (Figure 4) or a

single output at 26A (Figure 5). Multiple

LTM4620s can be combined to produce

from 50A to more than 100A (Figure 7).

impressive, but the promises made by these

claims are empty if the heat produced by

the supply is not effectively managed.

The LTM4620 solves the real power density

problem by squeezing a complete dual

output regulator into a 15mm × 15mm

× 4.41mm LGA package that is uniquely

designed to minimize thermal resistance

and thus simplify thermal manage-

ment. The package includes an internal

heat sink and other cutting edge fea-

tures that yield effective top and bot-

tom heat sinking, allowing it to run

(LTM4620, continued from page 1)

Claims of high power density can be impressive, but high power density is meaningless if the heat produced by the supply is not effectively managed. The LTM4620 solves the real power density problem by squeezing a complete dual output regulator in a package uniquely designed to simplify thermal management.

15mm

15mm

4.41mm

Figure 1. The LTM4620 LGA package includes thermal contacts on the top and bottom that connect to a unique internal heat sink, which keeps internal components cool by minimizing the internal thermal resistance.

PAY ATTENTION TO THE HEATUnwanted heat is a major challenge facing designers of high performance electronics systems. Modern processors, FPGAs, and custom ASICs dissipate increasing amounts of power as their temperature increases. To compensate for these power losses, power supplies must increase their power output. This, in turn, increases the power dissipation of the power supplies, contributing additional heat to an already hot system, and so on. Unless the heat is evacuated fast enough, the temperature of the entire system can elevate to the point where most components must be derated to compensate.

System and thermal engineers expend significant time and energy modeling and evaluating complex electronic systems to remove unwanted heat from the system. Fans, cold plates, heat sinks and even cooling bath submersion are all strategies that engineers have implemented to overcome the heat. Cooling size, weight, maintenance and cost become a significant portion of the engineering and manufacturing budget.

As systems add features and performance, the heat can only rise. Most processors and power supplies run about as efficiently as they can, and cooling systems are expensive mitigation. So simplification and cost savings must be found by improving power dissipation

at the component level. The problem is that most compact packaged power solutions either dissipate too much power or their thermal resistance is too high—there is no way to effectively remove enough heat to operate them at elevated temperature without significant derating.

POWER DENSITY NUMBERS NOT AS IMPRESSIVE AS THEY APPEARThe term high power density DC/DC regulator is misleading because it does not address the behavior of the device with respect to temperature. System designers often look to satisfy a watts/cm2 requirement, and power supply manufacturers are happy to oblige with impressive power density numbers. Even so, hidden in any device’s data sheet are temperature-related values that can be more important than the quoted power density.

For example, consider a 2cm × 1cm DC/DC regulator that delivers 54W to a load. This calculates to an impressive rated power density of 27W/cm2. This number should satisfy the power and size requirements of some designers. What’s often forgotten, though, is power dissipation, which translates into rising board temperature. The key piece of information is listed in the data sheet as the DC/DC regulator’s thermal

impedance, including the values for the package’s junction-to-case, junction-to-air and junction-to-PCB thermal impedances.

To continue with this example, this regulator has another attractive attribute: it operates at an impressive efficiency of 90%. Even at such high efficiency, it dissipates 6W while delivering 54W to the output in a package with 20ºC/W junction-to-air thermal impedance. Multiply 6W by 20ºC/W and the result is a 120ºC rise above the ambient temperature. At a 45ºC ambient temperature, the junction temperature of the package of this DC/DC regulator rises to 165ºC. This is far above the typical maximum temperature specified for most silicon ICs, which is roughly 120ºC. Using this power supply at its maximum rating would require extensive cooling to keep the junction temperature at a value below 120ºC.

Even if a DC/DC regulator addresses all of the electrical and power requirements of the system, if it fails to meet the basic thermal guidelines, or proves too costly when heat-mitigation measures are taken into account, all the impressive electrical specifications are moot. Evaluating the thermal performance of a DC/DC regulator can be as important as judging it on volts, amps and centimeters.

The Real Cost of Power Density


design features

thermal conductivity to both the top

and bottom of the device. Everything is

topped off with a proprietary internal heat

sink that attaches directly to the power

MOSFET stacks and the power induc-

tors for effective topside heat sinking.

The construction of the heat sink and

the mold encapsulation keeps the part

running cool even when thermal manage-

ment is simply forced air flow across the

top of the package. For a more robust

solution, an external heat sink can be

attached to the topside exposed metal

for even better thermal management.

Figure 2 shows a side view rendering

and a top view photo of an unmolded

LTM4620. The package consists of a highly

thermal conductive BT substrate with

adequate copper layers for current carry-

ing capacity and low thermal resistance

to the system board. The internal power

MOSFETs are stacked in a proprietary lead

frame to produce high power density,

low interconnect resistance, and high

UNIQUE PACKAGE DESIGN ACHIEVES TRUE HIGH POWER DENSITY

The LTM4620 is designed from the

ground up to produce dual or single

outputs at high power density with

easy-to-manage thermal characteristics.

Unlike other high power density solu-

tions, it is truly self-contained, requiring

no unwieldy heat sinks or liquid cool-

ing to run at maximum load current.

The internal power MOSFETs are stacked in a proprietary lead frame to produce high power density, low interconnect resistance, and high thermal conductivity to both the top and bottom of the device. Everything is topped off with a proprietary internal heat sink.

POWER MOSFET STACK

EFFECTIVE TOPSIDE HEAT SINKING

POWER INDUCTORS

EFFECTIVE BOTTOM HEAT SINKING

Figure 2. LTM4620 side view rendering and photo of an unmolded LTM4620 showing topside heat sink

AMBIENT TEMPERATURE (°C)0

LOAD

CUR

RENT

(A)

182022

120

1614

0

10

40 80 10020 60

12

8642

2624

400LFM200LFM0LFM

Figure 3. LTM4620 thermal image and derating curve

Go to video.linear.com/126 to see the impressive performance of the LTM4620. The videos here show real lab bench setup and measurement of short-circuit protection, thermal behavior and temperature rise at 26A and 100A, heat sink attachment and precision current sharing at start-up, steady state and shutdown.

See it in Action

http://video.linear.com/126


high power in tight spots, but it can do so

without contributing significantly to the

heat problem or requiring derating. Few, if

any other high power density solutions can

make this claim without adding expensive

heat-mitigating components and strategies.

DUAL 13A REGULATOR

Figure 4 shows a simplified block dia-

gram of the LTM4620 µModule regulator

in a dual output design. Its two internal

high performance synchronous buck

regulators produce 1.2V and 1.5V rails,

each with 13A load current capability.

The input voltage range is 4.5V to 16V.

The output voltage range of the LTM4620

is 0.6V to 2.5V, and 0.6V to 5.5V for

the LTM4620A. Total output accuracy

is ±1.5%, with 100% factory-tested

accurate current sharing, fast transient

response, multiphase parallel operation

with self-clocking and programmable

phase shift, frequency synchronization,

and an accurate remote sense ampli-

fier. Protection features include output

Figure 3 shows a LTM4620 thermal

image and a derating curve for a 12V to

1V at 26A design. The temperature rise

is only 35°C above ambient with no

heat sink and 200LFM of airflow. The

derating curve shows that maximum

load is available out to ~80°C, well

beyond the 65°C that the thermal image

shows for the full-running part.

This result reveals the real merits of a

thermally enhanced high density power

regulator solution. The unique package

design allows the part to not only produce

TEMP

CLKOUT

RUN1

MODE_PLLIN

PHASMD

TRACK1

= 100µA

4.7µF

CSS11µF

VINVIN

VIN

CIN222µF25V×2

RFB260.4k

MTOP1

MBOT1

POWERCONTROL

2.2µF

0.33µH

60.4k

COUT1

RFB140.2k

+VOUT11.5V/13A

VOUT21.2V/13A

VFB1

GND

GND

GND

GND

SW2

SW1

PGOOD2

PGOOD1

INTERNALCOMP

INTERNALFILTER

1µF

MTOP2

MBOT2

CIN422µF25V×2

2.2µF

0.33µH

COUT2+

+ –60.4k

VOUT1

VOUT2

VFB2

VOUTS2

VOUTS1

Rf(SET)121k

VINRT

VINRT

CSS2

DIFFOUT

DIFFN

DIFFP

COMP1

SGND

TRACK2

INTVCC

EXTVCC

RUN2

COMP2

fSET

SGND

INTERNALCOMP

Figure 4. Block diagram of the LTM4620 in a dual output, 1.5V/13A and 1.2V/13A, application

LTspice IVcircuits.linear.com/586

http://circuits.linear.com/586



design features

overvoltage protection feedback referred,

foldback overcurrent protection, and

internal temperature diode monitoring.

1.5V AT 26A IN 15mm2 WITH EASY THERMAL MANAGEMENT

Figure 5 shows a 1.5V at 26A solution that

combines the LTM4620’s two output chan-

nels in a parallel 2-phase design. The RUN,

TRACK, COMP, VFB, PGOOD and VOUT pins are

tied together to implement parallel opera-

tion. This design also features a LTC®2997

temperature sensor that monitors the

LTM4620’s internal temperature diode.

Figure 6 shows the 1.5V efficiency for

the 2-phase parallel output and the cur-

rent sharing of the two channels. 86%

efficiency is very good for such a high

density, high step-down ratio solution, and

thermal results are as good or better than

the 1V solution shown in Figure 3. The

temperature rise is well controlled due to

the low θJA thermal resistance after board

mount. Effective top and bottom heat

sinking enables the LTM4620 to operate

at full power with low temperature rise.

Figure 6 shows the well-balanced current

sharing of VOUT1 and VOUT2. The LTM4620’s

internal controller is accurately trimmed

and tested for output current sharing.

LTM4620

VIN

TEMP

RUN1RUN2

TRACK1TRACK

TRACK2

fSET

COUT2470µF6.3V

40.2k

5k

COUT1100µF6.3V

PHASMD

VOUT1

VOUTS1

SW1

VFB1

VFB2

COMP1

COMP2

VOUTS2

VOUT2

SW2

PGOOD2

MODE_PLLIN CLKOUT INTVCCEXTVCC PGOOD1

SGND GND DIFFP DIFFN DIFFOUT

COUT2470µF6.3V

COUT1100µF6.3V121k

10k*

D1*5.1V ZENER

0.1µF

22µF25V×4

4.7µF

+

+

* PULL-UP RESISTOR AND ZENER ARE OPTIONAL

INTVCC

LTC2997

A/D

µC1.8V

4mV/K470pF

0.1µF VCC

GND

VREF

VPTAT

D+

D–

VIN5V TO 16V

INTERMEDIATE BUS

VOUT1.5V AT 26A

Figure 5. The two outputs of the LTM4620 can be tied together to produce a 2-phase, 2-parallel-channel, design that yields 1.5V at 26A. Internal diode temperature monitoring is provided through the LTC2997.

EFFI

CIEN

CY (%

)

OUTPUT CURRENT (A)260

90

602 4 6 8 10 12 14 16 18 20 22 24

65

70

80

75

85

VOUT = 1.5VfSW = 550kHz

PER

CHAN

NEL

CURR

ENT

(A)

TOTAL OUTPUT CURRENT (A)260

14

02 4 6 8 10 12 14 16 18 20 22 24

12

10

8

6

4

2 IOUT1IOUT2

Figure 6. Efficiency and current sharing of 2-phase, single output 26A design shown in Figure 5


The LTM4620’s current mode archi-

tecture yields high efficiency and fast

transient response—top requirements

for low voltage core power supplies

for high performance processors, FPGAs

and custom ASICS. Outstanding initial

output voltage accuracy and the differ-

ential remote sensing result in accurate

DC voltage regulation at the load point.

The unique thermal capabilities of the

LTM4620 and its tight current sharing

capabilities make it possible to easily scale

the output above 100A (see Figure 7).

No external clock sources are needed

to set up multiphase operation—the

CLKIN and CLKOUT pins produce internal

programmable phase shifting for paral-

leled channels. The LTM4620 supports

either external frequency synchroniza-

tion or internal onboard clocking.

CONCLUSION

The LTM4620 µModule regulator is a true

high density power solution. It differen-

tiates itself in a the field of high power

density regulators because it manages

heat, the fatal flaw for many proclaimed

high density solutions. It features two high

performance regulators housed inside a

superior thermal package, which makes

possible high power designs that fit into

tight spaces—with minimal external

cooling. Built-in multiphase clocking and

factory-tested accurate current sharing

allow easy scaling of the output current to

25A, 50A, and 100A+. The LTM4620’s unique

thermal properties allow full power opera-

tion at elevated ambient temperatures. n

REAL POWER DENSITY: 100A IN UNDER 50mm2 WITH AIR COOLING

Figure 7 shows four µModule regula-

tors combined in parallel to produce an

8-phase, 100A design. Figure 8 shows

the balanced current sharing for all four

regulators. As shown in Figure 7 the

entire 100A solution only takes about 1.95

square inches of board space. Even at this

high current, a simple heat sink and air

flow can be applied across the top of all

four modules to remove enough power

loss to require no derating. Releasing

heat out of the topside also helps keep

the system board cool to minimize the

heating effect on other components.

Figure 8. Current sharing for the four LTM4620s combined in a 100A design shown in Figure 7

PER

µMod

ule

CURR

ENT

(A)

TOTAL OUTPUT CURRENT (A)1000

30

010 20 30 40 50 60 70 80 90

5

10

20

15

25

IOUT(µModule1)IOUT(µModule2)IOUT(µModule3)IOUT(µModule4)

Figure 7. Four µModule regulators combined in an 8-phase parallel design support 100A

The LTM4620 µModule regulator is a true high density power solution. It differentiates itself in a crowded field of “high power density” regulators because it manages heat, the fatal flaw for many proclaimed high density “solutions.”


design features

Multiple Power Sources No Problem for 1A, Low Noise Buck-Boost Converter with 1.8V–5.5V Input Voltage RangeGenesia Bertelle

The LTC3536 utilizes a proprietary switch-

ing algorithm that provides seamless

transitions between buck and boost modes

while simultaneously optimizing efficiency

and minimizing noise over all operating

conditions. This advanced control algo-

rithm uses only a single inductor, which

greatly simplifies the power supply design

and minimizes the total PCB footprint. As

a result, the LTC3536 easily fits lithium-

ion/polymer, 2-3 cell alkaline/NiMH and

lithium phosphate battery applications,

which often require a supply voltage that

is somewhere in the middle of the battery

voltage range. In such cases, the high effi-

ciency and extended input operating range

of the LTC3536 offer greatly improved

battery run time and design versatility.

DESIGN VERSATILITY

At 3.3V output, a load current of up

to 1A can be supported over the entire

lithium-ion input voltage range; 300mA of

load current is supported when the input

is 1.8V. The 1% accurate output volt-

age is programmable from 1.8V to

5.5V via an external resistor divider.

The switching frequency of the LTC3536 is

user programmable from 300kHz to 2MHz

via a single external resistor, allowing

the converter to be optimized to meet the

space and efficiency requirements of each

particular application. The default fre-

quency is set to 1.2MHz by tying the RT pin

to VIN. The switching frequency can also be

synchronized to an external clock applied

to the MODE/SYNC pin. In case of synchro-

nization, the free running frequency of the

oscillator can be programmed slower or

faster than the external clock frequency.

External resistors and capacitors pro-

vide compensation of the feedback

loop, enabling the frequency response

to be adjusted to suit a wide array

of external components. This flex-

ibility allows for rapid output voltage

transient response regardless of induc-

tor value and output capacitor size.

Depending on the application require-

ments, a designer can prioritize light load

efficiency or minimize supply noise by

choosing from two operating modes: Burst

Mode® operation and PWM operation,

which can be enabled via a dedicated pin.

Burst Mode operation is an efficient solu-

tion for low current conditions. It reduces

the amount of switching to the minimum

level required to support the load, thereby

minimizing the power supply switching

losses. Sometimes noise suppression is

of higher importance and PWM opera-

tion, though not as efficient as Burst

Mode operation at light loads, maintains

a steady frequency, making it easier to

reduce noise and RF interference. The

output current capability in Burst Mode

operation is lower than in PWM mode.

Therefore, higher load current applications

require that the MODE/SYNC pin be driven

externally to enter PWM mode operation.

The LTC3536 includes robust VOUT short

circuit protection. If VOUT is shorted to

ground, the inductor current decays very

slowly during a single switching cycle.

During a short-circuit condition, the

LTC3536 reduces its peak current limit

Users expect their portable devices to operate from a range of power sources including USB, wall adapters and various types of batteries—alkaline, lithium-ion and LiFePO4. The LTC®3536 monolithic synchronous buck-boost converter easily accommodates a variety of power sources by efficiently operating in both buck and boost modes from an input voltage range of 1.8V to 5.5V. No complicated topology is required to accommodate power source inputs above, below or equal to the output.

NOIS

E (d

Bm)

FREQUENCY (MHz)1.60

25

–750.2 0.4 0.6 0.8 1 1.2 1.4

–65

–55

–45

–35

–25

–15

–5

5

15 COMPETITIVE BUCK-BOOSTfSW = 1.3MHz

LTC3536fSW = 1MHz

Figure 1. Worst-case spectral comparison of the LTC3536 and typical competitor’s part. Note the much lower noise floor exhibited by the LTC3536 and its lower integrated subharmonic noise.


to a safe level and forces the device to

enter PWM mode, guaranteeing a smooth

recovery when the output short is released.

NOISE PERFORMANCE

Many applications are sensitive to noise

generated by switching converters. The

LTC3536 uses a low noise switching

architecture to reduce unwanted subhar-

monic frequencies. Subharmonic noise or

jitter is difficult to filter and can interfere

with other sensitive circuitry, and is most

prominent when VIN and VOUT are approxi-

mately equal. Some buck-boost converters

operating in this region produce pulse-

width and frequency jitter. The LTC3536

employs Linear Technology’s latest

generation buck-boost PWM modulation

circuitry, which dramatically minimizes

jitter, satisfying the demanding require-

ments of noise-sensitive RF applications.

Figure 1 shows worst-case spectral

comparisons of the LTC3536 (switch-

ing frequency 1MHz) and a competitive

buck-boost converter (switching fre-

quency 1.3MHz) that does not feature the

low noise architecture of the LTC3536.

The worst-case condition is achieved by

placing a fixed 1A load on the output and

slowly increasing or decreasing the input

voltage until the highest harmonic content

in the converter spectrum was observed.

The LTC3536 exhibits the expected

single large magnitude tone at its switch-

ing frequency of 1MHz, but note that

the total integrated noise is very low

when compared to the competition.

Remember, this test is specifically designed

to produce absolute worst-case sub-

harmonic peaks for the LTC3536—if the

input voltage is slightly higher or lower,

the magnitudes of the subharmonics are

much smaller. In contrast, in the compet-

ing buck-boost, there is less reduction in

subharmonic content over a much wider

input voltage range. Also, it exhibits a

much higher noise floor than the LTC3536,

indicative of significant pulse-width jitter

and potential noise interference issues.

SUPERCAPACITOR BACKUP POWER

The LTC3536 includes a soft-start circuit

to minimize the inrush current transient

during power-up. If at start-up the output

voltage is already pre-charged, the internal

soft-start is skipped and the LTC3536

immediately enters the mode of opera-

tion that has been set on the MODE pin. If

the MODE pin is tied high and Burst Mode

operation is selected, the output voltage is

regulated smoothly to the target voltage

value without discharging the output.

This feature makes the LTC3536 ideal for

supercapacitor-powered backup power

supply systems, as shown in Figure 2. In

this application, two series of superca-

pacitors are charged to 5V during normal

operation to provide the needed backup

energy in case the primary power fails.

As long as the primary power is pres-

ent, the LTC3536 remains in Burst Mode

operation with very low quiescent current,

minimizing drain on the backup storage

capacitor. The MODE pin is used to change

from Burst Mode to PWM mode opera-

tion when primary power is interrupted.

The LTC3536 utilizes a proprietary switching algorithm that provides seamless transitions between buck and boost modes while simultaneously optimizing efficiency and minimizing noise over all operating conditions. This advanced control algorithm uses only a single inductor, greatly simplifying power supply design and minimizing the total PCB footprint.

SW1VIN

SW2VOUT

FB

10µF

VSUPERCAP1.8V TO 5.5V

VC

LTC3536

4.7µH*

49.9k

866k

100k

330pF

10pF

MODE/SYNC

SHDN

RT182k

6.04k

*COILCRAFT XFL4020

PWM BURST

6.49k845k R2

R1

20k

20k

GND

VH UVOVVL

DIS

LTC2912-2

GND TMR

VCC

22µF

VSYS3.3V

300mA FOR VIN ≥ 1.8V1A FOR VIN ≥ 3V

0.1µF

47pF

CRT

MAIN POWER12V

DC/DCFigure 2. Supercapacitor-based backup power supply




design features

When the LED torch is switched on, the

LTC3536 is turned on via the SHDN pin to

supply 105mA constant load current to

the LED. Figure 4 shows the high efficiency

of this supply, enabling a slow discharge

of the two series 60F capacitors down to

1.8V. The LTC3536 regulates the output

and the LED current, guaranteeing light for

14 minutes if the supercap is charged up

to 5V. It is possible to extend this time by

increasing the supercap value or using a

battery with an adequate charge control.

CONCLUSION

The LTC3536 maintains an accurate

output voltage with input voltages above

or below the output. Its programmable

switching frequency and internal low

RDS(ON) power switches, in combina-

tion with low noise architecture, enable

the LTC3536 to offer high performance,

compact and highly efficient solutions. n

LTC3536 in backup mode can provide a

regulated 3.3V at a constant 1A load for

input voltages higher than 3V, and it can

operate down to VIN at 1.8V at a constant

300mA, while maintaining VOUT at 3.3V.

By covering the voltage range of the

supercapacitor, the supply maximizes

operating time, allowing systems enough

time to recover or perform housekeep-

ing tasks before shutting down.

SOLAR-POWERED LED DRIVER

The power generated by a solar cell var-

ies significantly with lighting conditions.

So a rechargeable storage device, such

a supercapacitor, is required to provide

continuous power when the solar cell

is insufficiently illuminated. Although it

has much less charge storage capacity

compared to a battery, a supercapacitor

requires significantly less maintenance,

is easy to charge and its cycle lifetime is

orders of magnitude longer than a battery.

The storage device can be combined with

the LTC3536 buck-boost DC/DC converter,

which is designed to simplify the task of

harvesting and managing energy from low

input voltage such as photovoltaic cells.

LTC3536 can work down to input voltages

as low as 1.8V, and provides very high

efficiency over a wide range of input volt-

ages above or below the output voltage.

Figure 3 shows an application for an

LED driver supplied with a solar cell for

an emergency LED torch. When the torch

is off, the LTC3536 is in shutdown. The

quiescent current of less than 1µA mini-

mizes supercapacitor drain when the

ambient light is no longer available.

The LTC3536 maintains an accurate output voltage with input voltages above or below the output. Its programmable switching frequency and internal low RDS(ON) power switches, in combination with low noise architecture, enable the LTC3536 to offer high performance, compact and highly efficient solutions.

EFFI

CIEN

CY (%

)

VIN (V)51.5

100

802 2.5 3 3.5 4 4.5

82

84

86

88

90

92

94

96

98VOUT = 2.9V

ILED = 200mAILED = 150mAILED = 105mAILED = 70mA

Figure 4. Efficiency of the solar panel application in Figure 3

SW1VIN

SW2VOUT

FB

10µF

60F

60F

1.8V TO 5.5V

VC

LTC3536

4.7µH*

49.9k

100k

220pF

10pF

MODE/SYNCSHDN

RT158k

221k

221k

2Ω*COILCRAFT XFL4020

6.49k1020k

GND

22µF

2.9V

47pFOFF ONPHOTOVOLTAIC

CELL

+

–LED

Figure 3. Solar panel application LTspice IVcircuits.linear.com/588



Surge Stopper with Ideal Diode Protects Input and OutputZhizhong Hou

The LTC4364 is a complete control solution

for load protection and output holdup in a

small footprint, eliminating bulky com-

ponents and undesirable voltage drops.

Figure 1 shows a functional block dia-

gram of the LTC4364. The part drives two

back-to-back N-channel pass transistors:

one protects against voltage surges and

maintains a regulated voltage to the out-

put (M1 in Figure 1), while the other acts

as an ideal diode for reverse input protec-

tion and output holdup (M2 in Figure 1).

The LTC4364 also guards against overloads

and short circuits, withstands output

voltage reversal, holds off the MOSFETs in

input undervoltage conditions and inhibits

turn-on or auto-retry in input overvolt-

age conditions. A shutdown mode reduces

the supply current to as low as 10µA.

Power systems in automobile and industrial applications must cope with short duration high voltage surges, maintaining regulation at the load, while protecting sensitive circuitry from dangerous transients. One common protection scheme involves a series iron core inductor and high value electrolytic bypass capacitor, augmented by a high power transient voltage suppressor (TVS) and fuse. This heavy-handed approach takes significant board real estate—the bulky inductor and capacitor are often the tallest components in the system. Even this protection scheme cannot protect against reverse input potentials or supply brownouts—possible scenarios in automotive environments. To protect against these events and maintain the output voltage, designers add a blocking diode, but the additional voltage drop in the diode increases power losses.

+–

–

+

TMR

50mV/25mV

+– 30mV

FB1.25V

SHDN

UV 1.25V

OVTIMER

–

+

– + – +IAVA

–+DA

20µA

10µA 12V12V

HGATE SOURCE DGATE

FLT

SENSE OUTVCC

CHARGEPUMP

ENOUT

GND

RSENSEM2M1OUTPUTINPUT

LTC4364

Figure 1. Simplified block diagram of the LTC4364


design features

ADVANCED SURGE STOPPER WITHSTANDS HIGHER VOLTAGES AND ENSURES SAFE OPERATION

Figure 2 shows a typical application of

the LTC4364. Under normal operating

conditions, the LTC4364 drives the surge

stopper N-channel MOSFET (M1) fully on

and regulates the VDS of the ideal diode

N-channel MOSFET (M2) to 30mV so that

the voltage drop from the input supply

to the load circuitry is minimized. Once

VOUT rises to 0.7V below VIN, the ENOUT pin

goes high to activate the load circuitry.

During an input voltage surge, the LTC4364

regulates the HGATE pin, clamping the

output voltage through MOSFET M1 and a

resistive divider so that the FB pin volt-

age is maintained at 1.25V. The load

circuit continues to operate, with little

more than a modest increase in sup-

ply voltage as illustrated in Figure 3.

In the case of a current overload, the

LTC4364 limits the output current through

M1 so that the voltage across the SENSE and

OUT pins is maintained at 50mV (when

OUT > 2.5V). For a severe output short

when OUT is below 1.5V, the current limit

sense voltage folds back to 25mV for addi-

tional protection of the MOSFET (Figure 4).

The timer capacitor ramps up whenever

output limiting occurs (either overvolt-

age as shown in Figure 5 or overcurrent).

If the condition persists long enough

for the TMR pin to reach 1.25V, the

FAULT pin goes low to give early warning

to downstream circuitry of impending

power loss. At 1.35V the timer turns off

the MOSFETs and waits for a cooldown

interval before attempting to restart.

The LTC4364 monitors voltage across

the MOSFET and shortens the turn-off

timer interval in proportion to increasing

VCC – VOUT. In this way a highly stressful

The LTC4364 is a complete control solution for load protection and output holdup in a small footprint, eliminating bulky components and undesirable voltage drops.

+

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR47nF

UVUV = 6V

D1CMZ5945B

68V

D31.5KE200A

MAX DC:100V/–24V

MAX 1msTRANSIENT:

200V

D4SMAJ24A

C10.1µF CHG

0.1µF

R42.2k

0.5W

OV = 60VOV ENOUT

FAULTENABLE

FLT

SHDN FB

R510Ω

R6100Ω

D51N4148W

VIN12V

R290.9k

1%

R1383k

1%

R310k1%

R7102k1%R84.99k1%

COUT22µF

VOUT4A CLAMPED AT 27V

M1FDB33N25

M2FDB3682

RSNS10mΩ

VCC

LTC4364

Figure 2. Surge stopper with reverse current protection withstands 200V/–24V transients at VIN.

50ms/DIV

CTMR = 6.8µFILOAD = 0.5A

VIN20V/DIV

12V

12VVOUT20V/DIV

92V INPUT SURGE

27V CLAMP (ADJUSTABLE)

Figure 3. The LTC4364 regulates output at 27V while load circuit continues to operate in the face of a 92V input spike.

VOUT (V)0

ΔV S

NS (m

V) 40

50

60

1.5 2.5 4.0

30

20

100.5 1.0 2.0 3.0 3.5

Figure 4. A 2:1 foldback of current limit reduces MOSFET stress upon severe output short.


output short-circuit condition lasts for a

shorter time interval than a brief, minor

overload, helping ensure the MOSFET oper-

ates within its safe operating area.

The LTC4364 features a very low restart

duty cycle of about 0.1% in either

overvoltage or overcurrent conditions,

ensuring the MOSFET cools down before

restarting following a turn-off caused by

fault. Figure 5 demonstrates the auto-

retry timer sequence of the LTC4364-2

following an overvoltage fault.

An important feature of the LTC4364 is

that a current limiting device such as a

resistor (R4 in Figure 2) can be placed

between the input supply and the VCC pin.

Now supply transients at the VCC pin can

be either filtered with a capacitor (C1 in

Figure 2) or clamped by a Zener diode

(D1 in Figure 2). If a proper MOSFET M1 is

selected, this scheme makes it possible to

withstand supply transients much higher

than 100V. The circuit in Figure 2 can

withstand supply transients up to 200V.

475k

VIN

UV = 6V

0V = 60V

10k

383k

100k

τUV = (383k||100k) • 10nFτOV = (475k||10k) •1nF

10nF

1nF

UV

LTC4364

OV

Figure 6. Input UV and OV monitors can be configured to block start-up into an overvoltage condition.

1.35V1.25V

FB

TMR

∆VHGATE

FLT

1.25V <1.25V

1st 2nd 31st0.15V

32nd

OV < 1.25V CHECKED

COOLDOWN PERIOD

Figure 5. The LTC4364-2 auto-retry timer sequence following an overvoltage fault provides a very long cooldown period (0.1% duty cycle).

1ms/DIV

VIN10V/DIV

DGATE10V/DIV

VOUT10V/DIV

12V

0V

0V

16.5V

12V

INPUT SHORTED TO GND

DGATE PULLS LOW

OUTPUT HELD UP

CLOAD = 6300µFILOAD = 0.5A

1ms/DIV

VIN20V/DIV

DGATE20V/DIV

VOUT20V/DIV

–24V

–24V

0V

0V

0V 0V

INPUT FORCED TO –24V

DGATE PULLS LOW

OUTPUT HELD UP

CLOAD = 6300µFILOAD = 0.5A

Figure 7. LTC4364 input protection: a. Upon an input short or brownout, the DGATE pin pulls low, shutting down the ideal diode MOSFET and holding up the output voltage.

b. In reverse input conditions, the DGATE pins pulls to the SOURCE pin, keeping the ideal diode MOSFET off and cutting off back feeding.

An important feature of the LTC4364 is that a current limiting device such as a resistor can be placed between the input supply and the VCC pin. Now supply transients at the VCC pin can be either filtered with a capacitor or clamped by a Zener diode. If a proper MOSFET is selected, this scheme makes it possible to withstand supply transients much higher than 100V.


design features

The LTC4364 also guards against overloads and short circuits, withstands output voltage reversal, holds off the MOSFETs in input undervoltage conditions and inhibits turn-on or auto-retry in input overvoltage conditions. A shutdown mode reduces the supply current to as low as 10µA.

INPUT VOLTAGE MONITORING PREVENTS UNWANTED TURN-ON

The LTC4364 detects input undervoltage

conditions such as low battery using the

UV pin, and keeps the MOSFETs off if the

UV pin voltage is below 1.25V. The LTC4364

also monitors input overvoltage conditions

and holds off the MOSFETs for start-up or

restart following an output fault condition.

At power-up, if the OV pin voltage is

higher than 1.25V before the 100µs

power-on-reset delay expires, or before

the UV pin voltage rises above 1.25V,

the MOSFETs remain off until the OV pin

voltage drops below 1.25V. This feature

allows prevention of start-up when a

board is inserted into an overvoltage

supply by using two separate resistive

dividers with appropriate filtering capaci-

tors for the OV and UV pins (Figure 6).

After start-up, under normal condi-

tions, a subsequent input overvoltage

condition does not turn off the MOSFETs,

but rather blocks auto-retry follow-

ing an output fault. If the OV pin volt-

age is above 1.25V when the cooldown

timer cycle ends following a fault, the

MOSFETs remain off until the input

overvoltage condition is cleared.

IDEAL DIODE PROTECTS AGAINST REVERSE INPUT AND BROWNOUT WITH MINISCULE VOLTAGE DROP

To protect against reverse inputs, a

Schottky blocking diode is often included

in the power path of an electronic system.

This diode not only consumes power

but also reduces the operating voltage

available to the load circuitry, particu-

larly significant with low input voltages,

such as during an automotive cold crank

condition. The LTC4364 eliminates the

conventional Schottky blocking diode and

its voltage and power losses by including

Figure 8. LTC4364 offers built-in output port protection against overvoltage, short or reverse voltage.

OUTSENSEDGATESOURCEHGATE

UV

OV

0.1µF

ENOUT

FLT

SHDN FB

R510Ω

VIN12V

R290.9k1%

R1383k1%UV

6V

OV60V R3

10k1%

*PROTECTED AGAINST BACKFEEDING OR FORWARD CONDUCTING FROM –20V TO 50V

VOUT*CLAMPEDAT 18V

M1FDB3632

M2FDMS86101

RSNS0.2Ω

CHG6.8nF

CIN10µF

10µF50VCER

10µF50VCER

VCC

LTC4364

GND TMR

R84.99k1%

R916.9k1%

RESR100mΩ

D2DDZ9702T15V

R749.9k1%

24V

12V

12V

23V

12V

OUTPUT FORCED TO 24V

DGATE PULLS LOW

INPUT DISCONNECTEDFROM OUTPUT

1ms/DIV

VIN20V/DIV

DGATE20V/DIV

VOUT20V/DIV –12V

–12V

12V

24V

12V

OUTPUT FORCED TO –12V

HGATE PULLS LOW

INPUT DISCONNECTEDFROM OUTPUT

1ms/DIV

VIN20V/DIV

HGATE20V/DIV

VOUT20V/DIV

Figure 9. LTC4364 output port protection: a. When output is forced above input, the DGATE pin pulls low to cut off back feeding.

b. When output is forced below the GND potential, the HGATE pin pulls to the SOURCE pin, cutting off forward conduction and saving battery power at input.


the DGATE pin to drive a second, reverse-

connected MOSFET (M2 in Figure 2).

In normal operating conditions, the

LTC4354 regulates the forward voltage

drop (VDS of M2) to only 30mV. If the

load current is large enough to result

in more than a 30mV forward volt-

age drop, M2 is driven fully on and

its VDS is equal to RDS(ON) • ILOAD.

In the event of an input short or a power

supply failure, reverse current temporar-

ily flows through M2. The LTC4364 detects

the reverse voltage drop and immediately

turns off M2, minimizing discharging of

the output reservoir capacitor and hold-

ing up the output voltage. Figure 7a shows

the result of a 12V input supply shorted

to ground. The LTC4364 responds to

this condition by pulling the DGATE pin

low, cutting off the reverse current path

so the output voltage is held up.

In a reverse battery connection, the

LTC4364 shorts the DGATE pin to the

SOURCE pin (that follows the input)

without the need of external compo-

nents, keeping M2 off and disconnect-

ing the load circuitry from the input

as shown in Figure 7b. The VCC, SHDN,

UV, OV, HGATE, SOURCE and DGATE pins

can all withstand up to 100V above

and 40V below the GND potential.

BUILT-IN OUTPUT PORT PROTECTION

When the output is on a connector as

shown in Figure 8, it could experience

overvoltage, short-circuit or reverse

voltage. The LTC4364 protects the load

circuitry and input supply against those

conditions with several features:

• If the output port is plugged into a

supply that is higher than the input,

the ideal diode MOSFET M2 turns

off to cut the back feeding path

open as shown in Figure 9a.

• If the output port is shorted to

ground, the HGATE pin first regu-

lates the forward current to the

current limit and then turns off

MOSFET M1 if the fault times out.

• If a reverse supply is applied to the

output port, the LTC4364 turns off

the pass MOSFET M1 once the OUT pin

voltage drops below the GND poten-

tial, cutting the forward conduct-

ing current path open and avoiding

battery drainage at the input.

Figure 9b shows the result when a

–12V supply is applied to the output. The

LTC4364 immediately shorts the HGATE pin

to the SOURCE pin (that follows output),

turning MOSFET M1 off so the input supply

is disconnected from the faulty output.

The OUT and SENSE pins of the LTC4364

can withstand up to 100V above and

20V below the GND potential. For appli-

cations where the output port could be

forced below ground, ceramic bypass

capacitors with proper voltage ratings

should be used at the output to stabilize

the voltage and current limiting loops

and to minimize capacitive feedthrough

of input transients (see Figure 8). A

low leakage diode (D2 in Figure 8)

should be used to protect the FB pin.

CONCLUSION

The LTC4364 is a compact and complete

solution to limit and regulate voltage and

current to protect sensitive load circuitry

against dangerous supply transients,

including those over 100V. It is an easy-to-

implement, high performance alternative

to the traditionally bulky protection cir-

cuits in automotive and industrial systems.

The LTC4364’s integrated ideal diode driver

holds up output voltage during input

short, supply brownout, or reverse input

while cutting the voltage loss associated

with blocking diodes. The built-in output

port protection is useful when the output

is on the connector side. Its feature set is

rounded out by input UV and OV monitor-

ing and a low current shutdown mode. n

The LTC4364 is a compact and complete solution to limit and regulate voltage and current to protect sensitive load circuitry against dangerous supply transients, including those over 100V.


design features

DC/DC Controller Combines Digital Power System Management with Analog Control Loop for ±0.5% VOUT AccuracyHellmuth Witte

DIGITAL POWER MANAGEMENT

In today’s data center systems the chal-

lenge is to “go green” by becoming as

efficient as possible at all levels of the

system—including the point of load, the

board, rack and even installation lev-

els. For instance, overall system power

consumption can be reduced by routing

the workflow to as few servers as possible,

shutting down servers that are not needed

at the time. The only way to do this and

meet system performance targets (compute

speed, data rate, etc.) is to implement a

comprehensive digital power manage-

ment system that monitors real-time

power-consumption data at all levels.

In the past, designers have cobbled

together digital power management solu-

tions using a grab bag of ICs including

supervisors, sequencers, DACs and ADCs.

In addition to the inherent complexity of

such solutions, they lack easy expandabil-

ity, requiring significant up front planning

for future system upgrades. The LTC3883/-1

eliminates this complexity by combining

all digital power management functions

in the DC/DC controller. The result is an

easy-to-use, robust and flexible point-of-

load (POL) power management solution.

The LTC3883/-1 can operate autonomously

or communicate via an industry-standard

I2C serial bus with a system host proces-

sor for command, control and to report

telemetry. This makes it possible to

monitor critical operating information

directly from the LTC3883/-1 such as real-

time voltages, currents and temperatures,

which can used to dynamically optimize

system performance and reliability.

Access to this data makes it possible to

predict power system failures and take

preventive or mediation measures.

Important regulator parameters—such

as output voltages and current limits,

margining voltages, overvoltage and

undervoltage supervisory limits, start-

up characteristics and timing and fault

responses—can also all be directly

The LTC3883/-1 is a versatile, single channel, PolyPhase® capable, buck controller with digital power system management, high performance analog control loop, on-chip drivers, remote output voltage sensing and inductor temperature sensing. To minimize solution size and cost, the LTC3883/-1 features Linear’s patent pending auto-calibration routine to measure the DC resistance of the inductor to obtain accurate output current measurements when the cycle-by-cycle current is measured across the inductor (lossless DCR sensing). The LTC3883/-1 is based on the popular dual channel LTC3880/-1, described in the January 2012 issue of LT Journal.

Figure 1. Digital power system management using the LTC3883.


The hallmark of the LTC3883 is an on-chip

LDO regulator for increased integration,

whereas the LTC3883-1 is powered from

an external 5V bias voltage for increased

efficiency. Both parts are available in a

thermally enhanced 32-lead 5mm × 5mm

QFN package with either a –40°C to 105°C

operating junction temperature range

(E-grade) or a –40°C to 125°C operating

junction temperature range (I-grade).

A 16-bit data acquisition system provides

digital read back of input and output

voltages and currents, duty cycle and

temperature. Peak values of important

measurements can be read back by the

user. Critical controller parameters can be

programmed via the PMBus. Fault log-

ging capability includes an interrupt flag

and a black box recorder in nonvolatile

memory that stores the operating con-

ditions immediately prior to a fault.

programmed via the serial bus, instead

of using external components such as

resistors, sequencers, and monitoring ICs.

Digital power system management

makes it possible to quickly and effi-

ciently develop complex multirail sys-

tems. Design is further simplified by

the LTpowerPlay™ software, which

enables PC-based board monitoring and

parametric adjustments. This allows a

designer to debug and perform in-circuit

testing (ICT) without any circuit board

rewiring or component modification.

FEATURE OVERVIEW

The LTC3883/-1 is a single output syn-

chronous step-down DC/DC controller

with integrated power FET gate drivers

and an analog current mode control loop

that is PolyPhase capable to six phases.

The frequency can be set from 250kHz

to 1MHz, and if an external oscillator is

available, the internal phase-locked loop

enables the LTC3883/-1 to synchronize with

any frequencies within the same range.

The LTC3883/-1 features optimized gate

driver dead times to minimize switch-

ing losses and body diode conduc-

tion, thus maintaining high efficiency

in all operating conditions. It supports

a wide VIN range of 4.5V to 24V and a

VOUT range of 0.5V to 5.5V. The precision

reference, 12-bit DAC, and temperature-

compensated analog current mode

control loop yield ±0.5% DC output

voltage accuracy, and an integrated high

side input current sense amplifier allows

for accurate input current sensing and

auto-calibration of the inductor DCR.

The LTC3883/-1 can operate autonomously or communicate via an industry-standard I2C serial bus with a system host processor for command, control and to report telemetry.

GND

0.1µF

1µF

10nF10nF

10µF

VIN6V TO 24V

1µF

5mΩ

10k

100Ω

2200pF

4.99k

22µF50V

+

D1

M1

M2

20k

12.7k

24.9k

9.09k

10k

23.2k

20k

17.8k

1.4k

VDD25

1.4k

VOUT1.8V20A

COUT530µF

0.22µF

100pF

D1: CENTRAL CMDSH-3TRL: VISHAY IHLP-4040DZ-11 0.56µH

M1: INFINEON BSC050N03LSGM2: INFINEON BSC011N03LSI

1.0µF1.0µF

0.56µH

TG

BG

PGND

FREQ_CFG

IIN_SNS BOOST

VIN_SNS

VIN

PGOOD

SW

INTVCC

LTC3883100Ω

10k

GPIO

10k

10k

SDA

10k

PMBusINTERFACE

VDD33

SCL

VOUT_CFG

VTRIM_CFG

ASEL

ISENSE+

ISENSE–

VSENSE+

VSENSE–

VDD25

VDD33

TSNSITH

10k

ALERT

10k

RUN

5k

SHARE_CLK

WP

SYNC

MMBT3906

10µF

1µF

COUT: 330μH SANYO 4TPF330ML, 2× 100µF AVX 12106D107KAT2A

3Ω

Figure 2. High efficiency 500kHz 1.8V step-down converter with DCR sense


design features

• System status

• Peak output current

• Peak output voltage

• Peak internal/external temperature

• Fault log status

ANALOG CONTROL LOOP

The LTC3883/-1 is digitally program-

mable for numerous functions includ-

ing the output voltage, current limit

set point and sequencing. The control

loop, though, remains purely analog,

offering optimum loop stability and

transient response without the quantiza-

tion effect of a digital control loop.

Figure 4 compares the ramp curves of

a controller IC with an analog feedback

control loop to one with a digital feed-

back control loop. The analog loop has

a smooth ramp, whereas the digital loop

has discrete steps that can result in stabil-

ity problems, slower transient response,

more required output capacitance in

some applications and higher output

ripple and jitter on the PWM control

signals due to quantization effects.

The current mode control loop produces

the best loop stability, cycle-by-cycle

current limit, and fast and accurate

responses to line and load transients.

The simple loop compensation is inde-

pendent of operating conditions and

converter configuration. Continuous,

discontinuous, and Burst Mode® induc-

tor current control are all supported.

• Overvoltage and undervoltage high

speed supervisor thresholds

• Output voltage on/off time delays

• Output voltage rise/fall times

• Input voltage on/off thresholds

• Output rail on/off

• Output rail margin high/margin low

• Responses to internal/external faults

• Fault propagation

The PMBus allow the user to monitor

the following power supply conditions:

• Output/input voltage

• Output/input current

• Internal die temperature

• External inductor temperature

• Part status

• Fault status

PMBus CONTROL

The LTC3883/-1 PMBus interface allows

digital programming of critical power

supply parameters as well as the read

back of important real-time conditions.

Parameter configurations can be down-

loaded to the internal EEPROM using Linear

Technology’s LTpowerPlay development

software. Figure 5 shows the PC-based

LTpowerPlay development platform

with a USB to I2C/SMBus/PMBus adapter.

Once a part is configured as desired,

it will operate autonomously without

control from the host, so no further

firmware or microcontroller is required.

The PMBus enables programming of the

following power supply parameters:

• Output voltage and margin voltages

• Temperature-compensated current limit

threshold based on inductor temperature

• Switching frequency

High performance PMBus controllers, such as the LTC3883/-1, and companion ICs, such as the LTC2978, work together efficiently and seamlessly to meet the strict digital power management requirements for today’s sophisticated circuit boards.

DC1890Socketed

Programming Board

DC1613AUSB to PMBus

Controller

DC1778ALTC3883

Demo Board

Customer Boardwith

LTC3883/LTC3883-1

SocketedProgramming

DemonstrationKit

In-Circuit SerialProgrammingoror

USB

Figure 3. Complete development platform with LTpowerPlay software


AUTO-CALIBRATION OF INDUCTOR DCR

Using the DC resistance of the inductor

instead of a sense resistor to sense the

output current of a DC/DC converter has

several advantages, including reduced

power loss, and lower circuit complex-

ity and cost. However, any difference

between the specified nominal inductor

DCR and the actual inductor DCR causes a

proportional error in the measured output

current, and in the peak current limit.

The tolerance of the inductor DCR from

its nominal value can be measured and

compensated for by the LTC3883/-1

using Linear’s patent pending algorithm.

Just complete a simple 180ms calibra-

tion procedure via PMBus command

while the converter is in a steady state

condition with a large enough load

current to allow for accurate input

and output current measurements.

The inductor temperature is accurately

measured by the LTC3883/-1 to maintain

an accurate current read back over the

entire operating temperature range. The

LTC3883 dynamically models the tempera-

ture rise from the external temperature

sensor to the inductor core to account

for the self-heating effect of the inductor.

This patent pending algorithm simplifies

the placement requirements of the exter-

nal temperature sensor and compensates

management circuitry cannot afford to

take up much PC board real estate.

High performance LTC PMBus controllers,

such as the LTC3883/-1, and companion

ICs, such as the LTC2978, work together

efficiently and seamlessly to meet the

strict digital power management require-

ments for today’s sophisticated circuit

boards. These include sequencing, voltage

accuracy, overcurrent and overvoltage

limits, margining, supervision and fault

control. Any combination of these devices

makes sequencing design an easy process

for any number of supplies. By using a

time-based algorithm, users can dynami-

cally sequence rails on and off in any

order with a simple programmable delay.

Sequencing across multiple chips is made

possible using the 1-wire SHARE_CLK bus

and one or more of the bidirectional

general purpose IO (GPIO) pins.

LTPOWERPLAY SOFTWARE

LTpowerPlay software makes it easy to

control and monitor multiple Linear

PMBus-enabled devices simultaneously.

Modify the DC/DC controller configura-

tion in real time by downloading system

parameters to the internal EEPROM of the

LTC3883/-1. This reduces design develop-

ment time by allowing system configura-

tions to be adjusted in software rather

than resorting to the draconian tasks

of swapping components and manually

rewiring boards. Figure 5 shows how

output voltage, OV/UV protection limits,

and on/off ramps are controlled. The

waveform displays the soft-start and

soft-stop of the output voltage. Warning

and fault conditions are also shown.

for the significant steady state and tran-

sient temperature error from the induc-

tor core to the primary heat sink.

MULTIPLE IC SYSTEMS

Large multirail power boards are normally

comprised of an isolated intermediate

bus converter, which converts –48V from

the backplane to a lower intermediate

bus voltage (IBV), typically 12V, which is

distributed around a PC card. Individual

point-of-load (POL) DC-DC converters step

down the IBV to the required rail voltages,

which normally range from 0.5V to 5V with

output currents ranging anywhere from

0.5A to 120A. These boards are densely

populated and the digital power system

Digital power system management makes it possible to quickly and efficiently develop complex multirail systems. Design is further simplified by LTpowerPlay software, which enables PC-based board monitoring and parametric adjustments.

FIXED fSW

FIXED fSW

DIGITAL CONTROL LOOP

ANALOG CONTROL LOOP

DIGITALRAMP

ANALOGCURRENT

WAVEFORM

Figure 4. The LTC3883’s analog control loop vs a digital control loop. The analog loop has a smooth ramp, whereas the digital loop has discrete steps that can result in stability problems, slower transient response, more required output capacitance in some applications and higher output ripple and jitter on the PWM control signals due to quantization effects.

LTpowerPlay software is available for free at www.llinear.com/ltpowerplay

LTpowerPlay

http://linear.com/ltpowerplay

http://linear.com/ltpowerplay


design features

LTpowerPlay software makes it easy to control and monitor multiple Linear PMBus enabled devices simultaneously. Modify the DC/DC controller configuration in real time by downloading system parameters to the LTC3883/-1 internal EEPROM.

margin testing is easily performed

using a couple of standard PMBus com-

mands. Combining the LTC3883/-1 with

other Linear PMBus products is the best

way to quickly bring to market digi-

tally controlled power supplies. n

All Linear PMBus products are sup-

ported by the LTpowerPlay software

development system, which helps

board designers quickly debug systems.

LTpowerPlay can be used to moni-

tor, control and adjust supply voltages,

limits and sequencing. Production

CONCLUSION

The LTC3883/-1 combines high perfor-

mance analog switching regulation

with precision data conversion and

a flexible digital interface. Multiple

LTC3883s can be used in parallel with

other devices to easily create optimized

multiple-rail digital power systems.

Figure 5. Power systems simplified. LTpowerPlay puts complete power supply control at your fingertips.


when there is a short circuit on the

output. It features DCM operation at

light load for lowest power consump-

tion and reverse current protection.

ROUT limits the output current during both

120W, 24V 5A OUTPUT BUCK-BOOST VOLTAGE REGULATOR

The buck-boost converter shown in

Figure 1 regulates 24V with 0A–5A load

at up to 98.5% efficiency (Figure 2). It

operates from an input voltage range

of 12V to 58V. Adjustable undervolt-

age and overvoltage lockout protect

the circuit. It has short-circuit protec-

tion and the SHORT output flag indicates

60V, 4-Switch Synchronous Buck-Boost Controller Regulates Voltage from Wide Ranging Inputs and Charges Batteries at 98.5% Efficiency at 100W+Keith Szolusha

The LT®3791-1 is a 4-switch synchronous buck-boost DC/DC converter that regulates both constant voltage and constant current at up to 98.5% efficiency using only a single inductor. It can deliver well over a hundred watts and features a 60V input and output rating, making it an ideal DC/DC voltage regulator and battery charger when both step-up and step-down conversion is needed. In addition to the high voltage, power and efficiency, it features short-circuit protection, a SYNC pin for synchronization to an external clock, a CLKOUT pin for driving an external SYNC pin or for parallel operation, OVLO (overvoltage lockout), SHORT output flag, C/10 detection and output flag for battery chargers, and a CCM pin for discontinuous or continuous conduction mode. The inclusion of DCM (discontinuous conduction mode) increases light load efficiency and prevents reverse current when it is undesirable.

VIN12V TO

58VINTVCC

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

RT

LT3791-1

SWI

SHORTC/10CCM

470nFIVINN

VIN

IVINP

IVINMONISMONCLKOUT

EN/UVLOOVLO

VREF

PWM

CTRL

147k200kHz

VCSYNCSS SGND

1µF

499k

56.2k

100k

499k

27.4k INTVCC

0.1µF

33nF

0.004Ω

ISPISNFB

0.1µF

L110µH

0.1µF

4.7µF

4.7µF50V×2

4.7µF100V

C147µF80V

ROUT7.5mΩ VOUT

24V5A

13.7k

38.3k

715k

+

COUT220µF35V×2

+

100k 200k

0.003Ω

51ΩD1

M1

M2

M4

M3

D2

D1, D2: NXP BAT46WJL1: COILCRAFT SER2915L-103KL 10µHM1, M2: RENESAS RJK0651DPB 60VdsM3, M4: RENESAS RJK0451DPB 40VdsC1: NIPPON CHEMICON EMZA800ADA470MJAOGCOUT: SUNCON 35HVT220M 35V 220µF ×2

33nF

10nF

15k1000pF

10k18.7k

Figure 1. 120W 24V 5A output buck-boost voltage regulator accepts a 12V–58V input




design features

a short circuit and an overload situa-

tion, making this a robust application.

The 14V, 10A voltage regulator in Figure 3

takes a slightly different approach. It runs

in CCM throughout its entire load cur-

rent range 0A-10A to provide the lowest

EMI at light load. It is still very efficient.

The circuit retains short-circuit protection

even though ROUT is replaced with a short.

The main switch sense resistor RSW limits

the short-circuit current at a higher level

than ROUT, but hiccup mode during short-

circuit limits the power consumption of

the IC, maintaining a low temperature

rise on the components during a short.

When DCM is not needed, ROUT may not

be necessary and removing ROUT slightly

increases circuit efficiency. OVLO is tied

to the output to limit the output voltage

transient during a 10A to 0A transition.

This protects both the output capacitors

and M3 and M4 switches from overvoltage.

The LT3791-1 can regulate both constant voltage and constant current. Large capacitive loads such as supercapacitors and batteries require constant current charging until they are charged up to a termination voltage, at which point they require constant voltage regulation. The LT3791-1 easily satisfies this requirement.

VIN9V TO

36V

INTVCC

CCM

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

OVLORT

LT3791-1

SWI

SHORTSHORT

C/10

470nF

IVINN VINIVINP

IVINMON

ISMONCLKOUT

EN/UVLO

VREF

PWM

CTRL

147k200kHz

VC

SYNC

SS

SGND

1µF499k

76.8k

INTVCC

0.1µF

22nF

0.0025Ω

ISPISN

FB

0.1µF

D1

M1

M2

M4

M5

M3

D2

L13.3µH

0.1µF

4.7µF10V

CIN14.7µF50V

COUT14.7µF50V×2

CIN2100µF63V×2

VOUT14V10A

499k

88.7k

100k

9.31k

+

COUT2270µF35V×2+

200k

0.002Ω

51Ω

100k

D1, D2: NXP BAT46WJL1: COILCRAFT SER2915H-332L 3.3µH 48AM1: RENESAS RJK0652DPB 60VdsM2: RENESAS RJK0651DPB 60VdsM3, M4: INFINEON BSC0904NSI 30VdsM5: NXP NX7002AKCOUT2: SUNCON 35HVT270MCIN2: NIPPON CHEMICON EMZA630ADA101MJAOG

10nF

5.1k100pF

Figure 3. 140W (14V, 10A) CCM buck-boost voltage regulator with 9V–56V input has output OVLO for transient protection.

LOAD CURRENT (A)0 1

EFFI

CIEN

CY (%

)

90

95

100

80

70

60

85

75

65

2 3 4 5

VIN = 12VVIN = 24VVIN = 54V

VIN = 14V IIN = 8.87A VOUT = 24V IOUT = 5A

Figure 2. Efficiency and worst case thermal results for the 24V converter in Figure 1


PARALLEL CONVERTERS FOR HIGH POWER USING CLKOUT AND SYNC

The LT3791-1 has a CLKOUT output that

can be used to synchronize other con-

verters to its own clock with a 180°

phase shift. By tying the CLKOUT of one

converter to the SYNC input of another,

the maximum output power is doubled

while the output ripple is reduced.

Figure 4 shows a 24V, 10A regulator

formed by running two LT3791-1s in paral-

lel. By using two parallel circuits, the max-

imum temperature rise seen on any one

discrete component is only 28°C on the M3

and M7 MOSFETs at the lowest VIN. The top

converter (master) in Figure 4 commands

the current level provided by the bottom

(slave) converter. The ISMON output of the

master indicates how much current the

master is providing, and by connecting

ISMON to the CTRL input of the slave, the

slave is forced to follow the master. A sin-

gle op amp is needed to provide the simple

200mV level shift needed to match the

CTRL input to the ISMON output levels. The

master converter runs in constant volt-

age regulation while the slave converter

is running in constant current regulation.

Note that the output voltage of the slave is

set slightly higher (28V) so that the voltage

feedback loop of the slave is not in regula-

tion for it to be able to follow the master.

VIN12V TO

58V

INTVCC

CCM

INTVCC1

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

RT

LT3791-1

SWISHORTSHORT

C/10

470nF

IVINN VINIVINP

IVINMON

ISMONCLKOUT

EN/UVLOOVLO

VREF

PWM

CTRL

147k200kHz

VC

SYNC

SS

SGND

1µF499k

56.2k

100k

499k

27.4k

INTVCC1

INTVCC1

0.1µF

33nF

33nF

0.004Ω

ISPISNFB

0.1µF

D1

M1

M2

M4

M3

D2

L110µH

0.1µF

4.7µF10V

4.7µF50V×2

4.7µF100V

C147µF80V

0.015Ω VOUT24V10A

13.7k

38.3k

715k

3.3k

10k

+

COUT1220µF35V×2+

200k

0.003Ω

51Ω

VIN

INTVCC

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

RT

LT3791-1

SWISHORTSHORT

C/10

470nF

0.22µF

IVINN VINIVINP

IVINMONISMON

SYNC

EN/UVLOOVLO

VREF

PWM

147k200kHz

VC

CTRL

SS

SGND

1µF

45k

499k

56.2k

100k

499k

27.4k

INTVCC2

INTVCC2

0.1µF

33nF

22nF

0.004Ω

ISPISNFB

0.1µF

D3

M5

M6

M8

M7

D4

L210µH

0.1µF

4.7µF10V

4.7µF50V×2

4.7µF100V

C247µF80V

0.015Ω

13.7k

38.3k

715k

2.2k

10k

+

COUT2220µF35V×2+

200k

0.003Ω

45k

51Ω

51Ω

0.47µF

51Ω

10k

–

+

1000pF

LTC6240

10k

D1–D4: NXP BAT46WJL1, L2: COILCRAFT SER2915L-103KL 10µHM1, M2, M5, M6: RENESAS RJK0651DPB 60VdsM3, M4, M7, M8: RENESAS RJK0451DPB 40VdsCOUT1, COUT2: SUNCON 35HVT220M ×2C1, C2: NIPPON CHEMICON EMZA800ADA470MJAOG

CCM

CLKOUT

Figure 4. Parallel LT3791-1s in a 240W application


design features

100W+ 2.5A BUCK-BOOST 36V SLA BATTERY CHARGER

The LT3791-1 can regulate both constant

voltage and constant current. Large

capacitive loads such as supercapacitors

and batteries require constant current

charging until they are charged up to a

termination voltage, at which point they

require constant voltage regulation. The

LT3791-1 easily satisfies this requirement.

As an example, the buck-boost converter

shown in Figure 5 charges a 36V 12Ah

SLA battery at 44V with 2.5A DC from a

9V-to-58V input. DCM operation prevents

reverse battery current when the out-

put load is overcharged, protecting the

circuit from large negative currents.

In some battery charger applications,

once termination voltage is reached and

charge current tails off, a standby or

float voltage regulation level is needed

that is different from the charge voltage.

The C/10 detection level of the LT3791-1

provides this capability. In the circuit

in Figure 3 the C/10 function drops the

battery voltage from charging (44V)

to float (41V) when the battery is near

full charge. When the battery voltage

is then pulled down from an increased

load, the voltage feedback loop returns

the charger to its charge state of 44V.

The LT3791-1 can be tailored to charge

a range of battery chemistries and

capacities from a variety of input sources

regardless of the voltage relationship

between them. Furthermore, a microcon-

troller can be used to create a maximum

power point tracking (MPPT) charger

from a solar panel. The output diag-

nostics ISMON and IVINMON and current

control pin CTRL make it easy to create a

high power solar panel battery charger.

DCM INCREASES EFFICIENCY AND PREVENTS REVERSE CURRENT

The LT3791-1 features both continuous

conduction mode (CCM) and discontinuous

conduction mode (DCM). Figure 6 shows

the difference between CCM and DCM. The

mode is selected by simply connecting

the CCM pin to either the INTVCC or C/10

pin. CCM provides continuous switching

50Ω

470nF

PVIN9V TO 57V

INTVCC

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

RT

LT3791-1

SWI

RIN0.003Ω

SHORT

IVINN

IVINP

1µFVIN

IVINMONISMON

CLKOUT

EN/UVLOOVLO

INTVCC

200k

VREFPWM

CTRLCHARGE CURRENT CONTROL

SGND

84.5k300kHz

D1, D2: BAT46WJL1: COILCRAFT SER2915L-103KM1-M4: RENESAS RJK0651DPBM5: NXP NX7002AKCIN2: ×2 NIPPON CHEMI-CON EMZA630ADA101MJA0GCOUT2: ×3 NIPPON CHEMI-CON EMZA630ADA101MJA0G

VCSYNCSS

CCM

C/10

10k

50Ω

INTVCC

24.3k

19.6k

332k

0.1µF

33nF

22nF

0.47µF

0.1µF

CIN2100µF63V×2

RSENSE0.004Ω

ISP

ISNFB

RBAT0.04Ω

2.5ACHARGE

36VSLA BATTERYAGM TYPE41V FLOAT44V CHARGE AT 25°C

0.1µF

0.1µF

L110µH

4.7µF

M2

M1

M3

M4

D2D1

COUT2100µF63V×3

COUT14.7µF50V×2

1.00M

30.1k402k

M53k

CIN14.7µF100V×2

+

10k

+

+

100k

Figure 5. SLA battery charger

The LT3791-1 features both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). CCM provides continuous switching at light load and inductor current can be either positive or negative. When the LT3791-1 enters DCM operation at light load, it prevents backward running current (negative inductor current) and light load power dissipation is minimized.


at light load and inductor current can

be either positive or negative. Although

zero-load inductor current in CCM is both

positive and negative and more power

is consumed than DCM, the switch node

ringing associated with DCM is elimi-

nated for those that do not want it.

When DCM is selected, the converter

remains in CCM until the load drops below

about 10% of the programmed maximum

output current. When the LT3791-1 enters

DCM operation at light load, the TG2 driver

for M4 stays low and M4 no longer runs

as a switch, but instead as a catch diode.

This prevents backward running cur-

rent (negative inductor current) and light

load power dissipation is minimized.

CONCLUSION

The LT3791-1 synchronous buck-boost

controller delivers over 100W at up to

98.5% efficiency to a variety of loads. Its

wide, 4.7V to 60V input range and 0V to

60V output range make it powerful and

versatile, and its built-in short-circuit

capabilities make for robust solutions

in potentially hazardous environments.

CCM and DCM operation make it use-

ful for highest efficiency or lowest noise

operation at light load. Its multiple control

loops make it ideal for regulating constant

voltage, constant current or both. This

feature-rich IC easily fulfills buck-boost

requirements where other topologies fail. n

VIN18V TO 55V

INTVCC

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2TG2

RT

LT3791-1

SWI

SHORTC/10CCM

470nFIVINN

VIN

IVINP

IVINMONISMONCLKOUT

EN/UVLOOVLO

VREF

PWM

CTRL

105k250kHz

VCSYNCSS SGND

1µF

499k

34.8k

100k

499k

28.7k INTVCC

0.1µF

1µF

22nF

0.1µF

0.005Ω

ISPISNFB

0.1µF

L122µH

0.1µF

4.7µF10V

CIN14.7µF100V

CIN2100µF80V×2

0.0125ΩVOUT48V3A

2.15k

2.49k

95.3k

40k

+

100k 200k

18.7k

0.004Ω

51Ω

10k

D1

M1

M2

M4

M3

D2

D1, D2: NXP BAT46WJL1: WÜRTH ELECTRONICS 74435572200 22µH 11AM1, M2, M4: RENESAS RJK0651DPB 60VdsM3: RENESAS RJK0652DPB 60VdsCOUT2: YAGEO ST 330µF 63V ×3 CIN2: NIPPON CHEMICON EMZA630ADA101MJAOG 100µF 63V ×2

1000pF

COUT14.7µF100V×2

COUT2330µF63V×3+

Figure 7. 48V application

c. DCM improves efficiency at light loads.

LT3791-1

CCM

C/10

INTVCCLT3791-1

CCM

INTVCC

100k

FOR DCM OPERATIONAT IOUT < 10mV/ROUT

FOR CCM OPERATIONOVER ALL IOUT

CCCMOPTIONAL

I LOA

D (m

A)VIN (V)

5412

5000

018 24 30 36 42 48

200

400

800

600

1000

DCM (TG2 FOR M4 STAYS LOW)

DCM FALLING THRESHOLD

CCM

CCM RISING THRESHOLD

POW

ER L

OSS

(W)

EFFI

CIEN

CY (%

)

IOUT (A)100.001

100

0

2

0 0.01 0.1 1

10

20

30

40

50

60

70

80

90

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8VIN = 24VVOUT = 24V

DCM DCMCCMCCM

EFFICIENCY

POWERLOSS

Figure 6. Overview of continuous conduction mode (CCM) for low noise and discontinuous conduction mode (DCM) for light load efficiency

a. DCM vs CCM setup b. DCM/CCM transition thresholds remain stable as the LT3791-1 moves through boost, buck-boost and buck modes of operation.


design features

100V Micropower No-Opto Isolated Flyback Converter in 5-Lead TSOT-23Min Chen

The LT8300 operates from an input

voltage range of 6V to 100V and deliv-

ers up to 2W of isolated output power.

The 150V integrated DMOS power switch

eliminates the need for a snubber in most

applications. By sampling the isolated

output voltage directly from the primary-

side flyback waveform, the LT8300 requires

no opto-coupler or transformer third

winding for regulation. The output volt-

age is set with a single external resistor.

Internal loop compensation and soft start

further reduce external component count.

Boundary mode operation at heavy load

enables the use of small magnetics and

produces excellent load regulation. Low

ripple Burst Mode operation maintains

high efficiency at light load while minimiz-

ing output voltage ripple. All these features

are packed in a 5-lead TSOT-23 package

(Figure 1) with high voltage pin spacing

conforming to IPC-2221 requirement.

PERFORMANCE AND SIMPLICITY

A complete isolated flyback solution

fits into an area less than 1 by ½ inch,

as shown in Figure 2. Figure 3 shows a

typical LT8300 application, generating a

5V isolated output from a 36V-to-72V input.

The solution only requires five external

components (input capacitor, output

capacitor, transformer, feedback resis-

tor and output diode) and two optional

undervoltage lockout resistors.

Although the LT8300 simplifies isolated

flyback converter design, it delivers

superior performance. Figure 4 shows

the power efficiency (85% peak) of the

5V application in Figure 3. Figure 5 shows

the load and line regulation (±0.5%) of

the 5V application in Figure 3. Figures

6 and 7 show its 50mA-to-250mA load

step transient and 1mA resistive load

start-up waveforms, respectively.

The non-synchronous flyback topology is widely used in isolated power supplies ranging from sub-watt power levels to tens of watts. Linear’s no-opto isolated flyback family dramatically simplifies isolated power supply design with proprietary primary-side sensing, which requires no opto-coupler or transformer third winding for output regulation. The new LT8300, the first micropower part in this family, significantly improves light load efficiency and reduces no-load input standby current to about 200µA.

Figure 1. The LT8300 is available in a 5-lead TSOT-23 package with high voltage pin spacing between pins 4 and 5.

Figure 2. The LT8300 isolated flyback converter solution size is less than 1 inch by ½ inch in a standard demo board DC1825A.


POST REGULATOR ELIMINATES OUTPUT TEMPERATURE VARIATION

The output voltage in a typical LT8300

application can be expressed as

V µA RN

VOUTFB

PSF=

−100 •

The first term in the VOUT equation does

not have temperature dependence, but

the output diode forward voltage VF has

a significant negative temperature coeffi-

cient (–1mV/°C to –2mV/°C). Such a negative

temperature coefficient produces approxi-

mately 200mV to 300mV voltage varia-

tion on the output across temperature.

For relatively high voltage outputs, say

12V and 24V, the output diode tempera-

ture coefficient has a negligible effect on

the output voltage regulation. But for

lower voltage outputs, such as 3.3V and

5V, the output diode temperature coef-

ficient contributes an additional 2%

to 5% output voltage regulation.

For designs requiring tight output voltage

regulation across temperature, a micro-

power low dropout linear regulator can be

added to post-regulate the LT8300 output.

The LT8300 should be programmed slightly

higher than the sum of the regulation

voltage and the LDO’s dropout voltage.

Figure 8 shows the LT8300 combined

with a LT3009-3.3 post-regulator to

generate a 3.3V/20mA isolated out-

put from an 18V-to-32V input. The

no-load input standby current is less

than 250µA as shown in Figure 9,

which conforms to DEF-STAN61-5.

By sampling the isolated output voltage directly from the primary-side flyback waveform, the LT8300 requires no opto-coupler or transformer third winding for regulation. The output voltage is set with a single external resistor.

LT8300

4:1

RFB

SW

300µH 19µH

EN/UVLO

1M

2.2µF

40.2k

VIN

VIN36V TO 72V

VOUT+

5V1mA TO 300mA

VOUT–

GND

210k

•

•

47µF

Figure 3. A 5V/300mA micropower isolated flyback converter from a 36V-to-72V input

LOAD CURRENT (mA)

OUTP

UT V

OLTA

GE (V

)

5.20

4.85

5.15

4.90

5.00

5.05

5.10

4.95

4.80300250200150100500

VIN = 36VVIN = 48VVIN = 72V

Figure 5. Output load and line regulation of the 5V application in Figure 3

LOAD CURRENT (mA)

EFFI

CIEN

CY (%

)

100

20

30

90

40

10

60

70

80

50

0300250200150100500

VIN = 48VVIN = 72V

VIN = 36V

Figure 4. Power efficiency of the 5V application in Figure 3

Figure 6. 50mA-to-250mA load step transient waveforms of the 5V application in Figure 3

500µs/DIV

VOUT500mV/DIV

VSW50V/DIV

IOUT100mA/DIV

Figure 7. 1mA resistive load start-up waveforms of the 5V application in Figure 3

500µs/DIV

VOUT5V/DIV

VSW50V/DIV

ILPRI100mA/DIV


design features

VARIOUS INPUT-REFERRED POWER SUPPLIES

In addition to isolated power supplies, the

LT8300 can be used in various nonisolated

applications. Two interesting applications

are input-referred positive and negative

power supplies often used for special gate

drivers. Figure 10 shows a simple VIN to

(VIN +10V) micropower converter, and

Figure 11 shows a simple VIN to (VIN – 10V)

micropower converter. In both of these

converters, the LT8300’s unique feedback

sensing scheme is used to easily develop

an output voltage that tracks VIN.

CONCLUSION

The LT8300 greatly simplifies the design

of isolated flyback converters, improves

light load efficiency and reduces no-load

input standby current when compared

to traditional schemes. The high level

of integration and the use of boundary

and low ripple burst modes results in

a simple to use, low component count,

and high efficiency solution for isolated

power supplies, as well as various spe-

cial nonisolated power supplies. n

The LT8300 greatly simplifies the design of isolated flyback converters, improves light load efficiency and reduces no-load input standby current when compared to traditional schemes.

LT8300 D1

Z1

RFB

SW

L1330µH

EN/UVLO

1M

1µF

118k

VIN

VIN15V TO 80V

VOUT+

10V50mA

VOUT–

GND

102k

L1: COILTRONICS DR73-331-RD1: DIODES INC. SBR1U150SAZ1: CENTRAL CMDZ12L

4.7µF

LT8300 D1

Z1

RFB

SW

L1330µH

EN/UVLO

1M

1µF

118k

VIN

VIN15V TO 80V VOUT

+

10V100mA

VOUT–

GND

102k

L1: COILTRONICS DR73-331-RD1: DIODES INC. SBR1U150SAZ1: CENTRAL CMDZ12L

4.7µF

Figure 11. A VIN to (VIN – 10V) micropower converterFigure 10. A VIN to (VIN + 10V) micropower converter

VIN (V)

I VIN

(µA)

400

200

300

100

0323028262420 2218

Figure 9. No-load input standby current of the 3.3V application in Figure 8

LT8300

L11:1

D1

RFB

SW

150µH 150µH

EN/UVLO

1M

1µF

93.1k

VIN

VIN18V TO 32V

VOUT+

3.3V0mA TO 20mA

VOUT–

GND

42.2k D1: DIODES INC. SBR0560S1-7L1: DRQ73-151-RZ1: CENTRAL CMDZ4L7

•

•

1µF 1µFZ1

LT3009-3.3

GND

SHDN

IN OUT

Figure 8. A 3.3V/20mA micropower isolated converter from an 18V-to-32V input conforming to DEF-STAN61-5


Battery Chargers, Bipolar Supplies and LED Drivers

• LT3796: Boost LED driver with

short-circuit protection and current

monitor (9V–60V to 85V LED string at

400mA) www.linear.com/LT3796

• LTC3260: Low noise ±12V power supply

from a single 15V Input (15V to ±12V at

50mA) www.linear.com/LTC3260

• LTM8062A: 2A, 4-cell Li-ion battery

charger (18V–32V to 16.4V at 2A)

www.linear.com/LTM8062

Currrent Sense Amplifiers

• LT1787: Bidirectional current sense

amplifier with offset bipolar

output www.linear.com/LT1787

• LT6105: Unidirectional current sense

amplifier for negative supplies

www.linear.com/LT6105

• LT6106: Single supply, unidirec-

tional current sense amplifier

www.linear.com/LT6106

High Speed Amplifiers and Resistor Networks

• LT5400: Quad matched resistor

network www.linear.com/LT5400

• LTC6417: 1.6GHz low noise high

linearity differential buffer/16-bit

ADC driver www.linear.com/LTC6417

Energy Harvesting

• LTC3109: Auto-polarity, ultralow

voltage step-up converter and power

manager www.linear.com/LTC3109

• LTC3588-2: Piezoelectric energy harvesting

power supply with 14V minimum

VIN www.linear.com/LTC3588-2

Step-Down Regulators

• LT3975: 42V, 2.5A, 2MHz step-down

switching regulator with 2.7µA quiescent

current www.linear.com/LT3975

• LT3976: 40V, 5A, 2MHz step-down

switching regulator with 3.3µA quiescent

current www.linear.com/LT3976

• LTC3605A: 20V, 5A synchronous step-down

regulator www.linear.com/LTC3605A

• LTC3626: 20V, 2.5A synchronous

monolithic step-down regulator with

current and temperature monitoring

www.linear.com/LTC3626

• LTM4620: Dual 13A or single

26A DC/DC µModule regulator

www.linear.com/LTC4260

Multi-Topology Regulators

• LT3758A: HV, boost, flyback, SEPIC and

inverting controller with improved

transient www.linear.com/LT3758

What’s New with LTspice IV?Gabino Alonso

Overvoltage Protection and Pushbutton Controllers

• LT4363-2: Overvoltage

regulator with 250V surge protec-

tion (5.5V–250V to 16V clamped

output) www.linear.com/LT4363

• LTC2955: Pushbutton on/off

control with auto turn-on at

12V (12V or battery backup to 3.3V at

20mA) www.linear.com/LTC2955

Step-Down Regulators

• LT3988: Dual 60V step-down regulator

(7V–60V to 5V at 1A and 3.3V at

1A) www.linear.com/LT3988

• LT3992: FMEA fault tolerant dual

converter (7V–60V to 5V at 2A and

3.3V at 2A) www.linear.com/LT3992

• LT8611: µPower synchronous step-down

regulator with current sense (3.8V–42V to

3.3V at 2.5A) www.linear.com/LT8611

• LTM4620: High efficiency 8-phase

100A step-down regulator (4.5V–16V to

1V at 100A) www.linear.com/LTM4620

• LTM8026: Two 2.5V series super capacitor

charger (7V–36V to 5V at 5.6A)

www.linear.com/LTM8026

LTspice® IV is a high performance SPICE simulator, schematic capture and waveform viewer designed to speed the process of power supply design. LTspice IV adds enhancements and models to SPICE, significantly reducing simulation time compared to typical SPICE simulators, allowing one to view waveforms for most switching regulators in minutes compared to hours for other SPICE simulators.

LTspice IV is available free from Linear Technology at www.linear.com/LTspice. Included in the download is a complete working version of LTspice IV, macro models for Linear Technology’s power products, over 200 op amp models, as well as models for resistors, transistors and MOSFETs.

What is LTspice IV?

Follow @LTspice on Twitter for up-to-date information on models, demo circuits, events and user tips: www.twitter.com/LTspice

NEW DEMO CIRCUITS NEW MODELS

http://www.linear.com/LT3796

http://www.linear.com/LTC3260

http://www.linear.com/LTM8062







http://www.linear.com/LTC3588-2



http://www.linear.com/LTC3605A









http://www.linear.com/4620

http://www.linear.com/LTM8026

http://www.linear.com/LTspice

http://www.twitter.com/LTspice


design ideas

• LT3957A: Boost, flyback, SEPIC and

inverting converter with 5A, 40V switch

www.linear.com/LT3957A n

PIECEWISE LINEAR FUNCTION FOR VOLTAGE OR CURRENT SOURCES

Piecewise linear (PWL) functions are used to construct a waveform from a series of straight line segments connecting points defined by the user. Since PWL functions are useful in creating custom waveforms, they are typically used in defining voltage or current sources.

To add a PWL function to a voltage or current source:

1. Right-click on the symbol in the schematic editor

2. Click Advanced

3. Select either PWL(t1, v1, t2, v2…) or PWL File:

4. Depending on your choice in step 3, either enter the PWL values or choose a file.

If you choose to enter the values directly, the PWL statement will be built from your values. The syntax of a PWL statement is a list of two-dimensional points that represent time and value data pairs where the time value is in ascending order:

PWL (0 0 1m 1 2m 1 3m 0)

Time values can also be defined relative to the previous time value by prefixing the time value with a + sign:

PWL (0 0 +1m 1 +1m 1 +1m 0)

Here’s an example of the nonrelative value pairs in the dialog:

The list of two-dimensional points that represent time and value data pairs can be encapsulated in a file and used in a PWL statement:

PWL (file=data.txt)

Other Forms of PWL Statement

LTspice IV supports many other forms of PWL statement. To explore these you will have to directly edit your statement by right-clicking on the text line with the PWL statement (not the component symbol), in the schematic editor. Some examples of alternate PWL forms:

•Repeating data pairs a specified number of cycles, or forever:

PWL REPEAT FOR 5 (0 0 1m 1 2m 1 3m 0) ENDREPEAT

PWL REPEAT FOREVER (0 0 1m 1 2m 1 3m 0) ENDREPEAT

•A trigger expression that turns the source on as long as the expression is true:

PWL (0 0 1m 1 2m 1 3m 0) TRIGGER V(n003)>1

•Scaled time or source values:

PWL TIME_SCALE_FACTOR=0.5 VALUE_SCALE_FACTOR=2 (0 0 1m 1 2m 1 3m 0)

Try using one of these forms of PWL expressions in your next simulation.

Happy simulations!

Power User Tip

SCHEMATIC EDITOR SHOWS COMPONENT WITH ATTACHED PWL STATEMENT

FILE WITH PWL DATA

WAVEFORM PRODUCED BY THE PWL STATEMENT

PWL functions are an easy way to create a custom waveform, typically used to define values for a voltage or current source

http://www.linear.com/LT3957A


and sending power through to the output.

Thus R3 and D1 are critical to start-up.

Under normal operating conditions the

GATE pin limits itself to about 12.5V above

the output, so with 12V at the input,

Q1’s gate is biased to 24.5V and Q2’s gate

is biased slightly lower, about 24V.

When the input is subjected to a high

voltage transient, R3 and D1 pull up on

the gate of Q2, which in turn is clamped

by D2 to approximately 80V. Acting as

a source follower, Q2’s source rises no

further than about 75V, keeping VCC and

SNS safely below their 100V maximum

rating. Unlike the shunt clamped applica-

tion shown in Figure 2, the series clamped

topology of Figure 3 permits full use of

the LT4356’s current limiting feature. Q1

regulates in the normal way, limiting the

output voltage as prescribed by R1 and R2.

An added benefit of the topology shown

in Figure 3 is that Q2 shares SOA stress

with Q1. For inputs in the range of

150V to 200V, the SOA stress is shared

equally between Q1 and Q2. In certain

applications this allows two inexpensive

The LT4356 surge stopper is a dramatic

performance upgrade over traditional,

passive clamp protection techniques. It

actively protects downstream components

from overvoltage by regulating the gate

of a pass MOSFET and it limits current

with the help of a standard sense resistor.

Figure 1 shows a typical 12V application.

The LT4356 has a rated maximum of

100V with an operating voltage range

of 4V to 80V, making it ideal for pro-

tecting downstream electronics in a

wide variety of industrial and automo-

tive applications. Nevertheless, some

circuits require protection against

transients as high as 200V to 300V.

Figure 2 shows one way that the LT4356

can be made to suppress such high volt-

ages, but at the cost of the current limiting

feature. In Figure 2 the VCC and SNS pins

are decoupled from the raw input voltage

and separately clamped to a safe value

below 100V. Since the VCC and SNS pins are

of necessity disconnected from the input

path, current sensing is not possible and

the circuit serves only as a voltage clamp.

It is possible to overcome this limitation

by cascading a second pre-regulating

MOSFET, Q2, as shown in Figure 3. Q2

clamps the VCC and SNS pins to a safe

level, restores the current limit fea-

ture and as an added benefit, shares

SOA (safe operating area) stress with Q1.

When power is first applied, R3 and D1

pull up on the gate of Q2, which in turn

passes power through to the LT4356. The

GATE pin then pumps up the gates of Q1

and Q2, fully enhancing both MOSFETs

100V Surge Stopper Protects Components from 300V TransientsHamza Salman Afzal

High voltage transients in automotive and industrial systems are common and can last from microseconds to hundreds of milliseconds, sending significant energy downsteam. Transient causes include automotive load dumps, and spikes caused by load steps and parasitic inductance. To avoid the risk of failure, all electronics in these systems must either be robust enough to directly withstand the transient energy spikes, or they must be protected from them.

0.1µF

10Ω

10mΩ IRLR2908VIN12V

LT4356DE-1

GND TMR

OUTGATESNS

IN+SHDN

AOUTFAULT

VOUT

EN

FLTUNDERVOLTAGE

FB

VCC

DC-DCCONVERTER

GNDSHDN

VCC

4.99k

383k

100k

102k

Figure 1. 12V overvoltage regulator

CTMR0.1µF

Q1IRF640

VIN24V

VOUTCLAMPEDAT 32V

LT4356DE-1

GND TMR

OUTSNS

SHDN

FLTEN

VCC FBD2*

SMAT70A 4.99k

118k

GATE

10Ω

1k1W

*DIODES INC.

Figure 2. 24V application circuit capable of withstanding 150V


design ideas

MOSFETs to replace a single, and much

more costly, special high SOA device. As

the peak input voltage requirement rises

above 200V, the SOA becomes increas-

ingly concentrated in Q2 and the series

connection offers no substantial relief.

Figure 4 shows a complete circuit based

on the new topology, designed to with-

stand up to 300V peak input. As previously

described, Q2’s gate is clamped at 80V so

that with a 300V input, Q2 drops 225V,

while Q1 sees no more than 75V total. For

this reason a 250V device is specified for

Q2, and a 100V device suffices for Q1. It is

possible to withstand even higher input

voltages by appropriate selection of Q2.

When designing circuits to withstand

such high input voltages, it is important

to recognize the potential for high dV/dt

at the input and resulting consequences.

Until the circuit can respond, current

arising from an instantaneously applied

high input voltage is limited only by

the parasitic inductance and the path

resistance to the output capacitor. While

most test waveforms specify some suf-

ferable rise time, an infinite input slew

rate is not inconceivable, such as might

arise during bench testing. Q3 is added

to give the LT4356’s current limit loop

a head start under these conditions.

Figure 5 shows the results of the cir-

cuit subjected to a 300V spike. CTMR is

sized to ride through such excursions,

but longer duration surges will be

interrupted, thereby protecting the

MOSFETs from certain destruction. n

The LT4356 has a rated maximum of 100V with an operating voltage range of 4V to 80V, but a little extra circuitry enables it to protect against transients as high as 300V.

2ms/DIV

INPUT50V/DIV

OUTPUT20V/DIV

CTMR

RSNS Q1Q2VIN12V

VOUT

LT4356

GND TMR

OUTSNSVCC

FB

D280V

R2

R1

GATED1 D3

R3

Figure 3. Pre-regulator topology extends protection range of the LT4356. Figure 4 shows the complete circuit.

CTMR0.1µF

RSNS33mΩ

RSNUB51Ω

CSNUB0.01µF

Q1FQB55N10

Q2FDB33N25

VINMAX RANGE: 0V–300V

OPERATING RANGE: 9V–16V

VOUT1.5A LOAD CURRENT16V REGULATION

LT4356

GND TMR

OUTSNSVCC

SHDN

AOUTIN+ EN

FLT

FB

D41N756A

D2SMAJ70A*

R215k

R1178kGATE

Q32N3904D1

1N4148D3

1N4148

10Ω10ΩR310k

100Ω

10k

0.039µF

100µF

0.1µF

*DIODES INC.

+

Figure 4. 16V overvoltage regulator capable of blocking 300V transients Figure 5. Results of 300V spike on input of circuit in Figure 4


application with PWM dimming. The

LT3761 uses the same high performance

PWM dimming scheme as the LT3755/LT3756

family, but with the additional feature

of the internally generated PWM dim-

ming signal and no additional pins.

INTERNAL PWM DIMMING GENERATOR

Unlike other high power LED drivers, the

LT3761 can generate its own PWM dim-

ming signal to produce up to 25:1 dim-

ming. This enables it to produce accurate

PWM dimming without the need for

external PWM-generating components. The

Accurate PWM LED Dimming without External Signal Generators, Clocks or µControllersKeith Szolusha

The LT3761 combines the simplicity of

analog dimming with the accuracy of

PWM dimming by generating its own

PWM signal. High dimming ratios are

possible by adjusting a simple DC signal

at its dimming input—no additional

PWM-generating microcontrollers, oscil-

lators or signal generators are required.

The LT3761’s internal PWM signal

can produce 25:1 dimming, while it

can still deliver up to 3000:1 dim-

ming with an external PWM signal.

HIGH POWER LED DRIVER

The LT3761 is a high power LED driver

similar to the LT3755-2 and LT3756-2

family. It is a 4.5V-to-60V input to

0V-to-80V output single-switch con-

troller IC that can be configured as a

boost, SEPIC, buck-boost mode or buck

mode LED driver. It has a 100kHz to

1MHz switching frequency range, open

LED protection, extra internal logic to

provide short-circuit protection, and can

be operated as a constant voltage regula-

tor with current limit or as a constant-

current SLA battery or supercap charger.

Figure 1 shows a 94% high efficiency 60V,

1A (60W) 350kHz automotive headlamp

LEDs can be dimmed in two ways: analog and pulse-width modulation (PWM) dimming. Analog dimming changes LED light output by simply adjusting the DC current in the string, while PWM dimming acheives the same effect by varying the duty cycle of a constant current in the string to effectively change the average current in the string. Despite its attractive simplicity, analog dimming is inappropriate for many applications because it loses dimming accuracy by about 25%+ at only 10:1 brightness levels, and it skews the color of the LEDs. In contrast, PWM dimming can produce 3000:1 and higher dimming ratios (at 100Hz) without any significant loss of accuracy, and no change in LED color.

VIN

LT3761

L110µH

RTVC INTVCC

EN/UVLO

FB

VREF SENSE1M

100k

INTVCC

INTVCC

499kCIN2.2µF×2100V

CC4.7nF

CSS0.01µF

CPWM47nF

300Hz

COUT2.2µF×4

VIN8V TO

60V

RDIM124k

90.9k

RC5.1k

RT28.7k350kHz CVCC

1µF

140k

CTRLRSENSE10mΩ

M1

D1

M2

M1: INFINEON BSC123N08NS3-GD1: DIODES INC PDS5100L1: COILTRONICS HC9-100-RM2: VISHAY SILICONIX Si2328DSCOUT, CIN: MURATA GRM42-2X7R225K100R

(CURRENT DERATED FOR VIN < 10V)

1M

16.9k

OPENLEDDIM/SSDIMPWM

GND

ISPISN

GATE

PWMOUT

RLED0.25Ω

1A

60WLEDSTRING

Figure 1. 94% efficient boost LED driver for automotive headlamp with 25:1 internal PWM dimming


design ideas

from a microcontroller to obtain very

high dimming performance. The practi-

cal minimum duty cycle using the inter-

nal signal generator is about 4% if the

DIM/SS pin is used to adjust the dimming

ratio. For 100% duty cycle operation,

the PWM pin can be tied to INTVCC.

CONCLUSION

The high power and high performance

LT3761 LED driver has its own onboard

PWM dimming signal generator that

is both accurate and easy to use. n

LT3761 requires only an external DC volt-

age, much like analog dimming control,

for high performance PWM dimming at

a chosen frequency. It can still receive a

PWM input signal to drive the LED string

with that signal in standard fashion.

The internal PWM dimming signal

generator features programmable

frequency and duty cycle. The fre-

quency of the square wave signal at

PWMOUT is set by a capacitor CPWM from

the PWM pin to GND according to the

equation: fPWM = 14kHz • nF/CPWM. The

duty cycle of the signal at PWMOUT is set

by a µA-scale current into the DIM/SS pin

as shown in Figure 3. Internally gener-

ated pull-up and pull-down currents

on the PWM pin are used to charge and

discharge its capacitor between the high

and low thresholds to generate the duty

cycle signal. These current signals on the

PWM pin are small enough so they can

be easily overdriven by a digital signal

ILED1A/DIV

0.5ms/DIV

VDIM = 7.7VDCPWM = 96%

VDIM = 4VDCPWM = 50%

VDIM = 1.5VDCPWM = 10%

VDIM = 0.4VDCPWM = 4.3%

Figure 2. Internally generated PWM signal and LED current for the application in Figure 1

200ns/DIV

PWMINPUT

PWMOUT5V/DIV

CPWMOUT = 2.2nF

Figure 4. Given a high speed PWM input signal, the LT3761 still provides a high speed PWMOUT signal.

DIM/SS CURRENT (µA)–10

PWM

OUT

DUTY

RAT

IO (%

)

100

60

20

80

40

020 4010 300 50

Figure 3. Setting the duty cycle at the DIM/SS pin takes a µA-scale signal. This pin can also be used with an external PWM signal for very high dimming ratios.

The LT3761 generates its own PWM signal to achieve accurate PWM dimming, but with the simple control of analog dimming. High dimming ratios are possible by adjusting a simple DC signal at its dimming input—no additional PWM-generating microcontrollers, oscillators or signal generators are required.


The LTC4290/LTC4271 fourth gen-

eration PSE controller supports fully

compliant IEEE 802.3at operation,

while minimizing heat dissipation

through the use of low RDS(ON) external

MOSFETs and 0.25Ω sense resistors.

Eliminate Opto-Isolators and Isolated Power Supply from Power over Ethernet Power Sourcing EquipmentHeath Stewart

The IEEE standard also defines PoE termi-

nology. A device that provides power to

the network is known as power sourc-

ing equipment (PSE), while a device

that draws power from the network

is known as a powered device (PD).

The LTC4290/LTC4271 PSE controller chip-

set revolutionizes PSE architecture by delet-

ing the customary digital isolation and

removing an entire isolated power supply.

Instead, the chipset employs a propri-

etary isolation protocol using a low cost

Ethernet transformer pair, leading to a sig-

nificant reduction in bill of materials cost.

Power over Ethernet (PoE), is defined by the IEEE 802.3at specification to safely deliver application power over existing Ethernet cabling. Implementation of Power over Ethernet requires careful architecture and component selection to minimize system cost, while maximizing performance and reliability. A successful design must adhere to IEEE isolation requirements, protect the Hot Swap™ FET during short-circuit and overcurrent events, and otherwise comply with the IEEE specification.

PSE PD

+

1500V ISOLATION

PSECONTROLLER

HOST

PHY

PDCONTROLLER

PHY

ISOLATEDDC/DC

CONVERTER

ISOLATEDDC/DC

CONVERTER

Figure 1. Traditional PSE isolation schemes require a number of opto-isolators and a cumbersome, and costly isolated DC/DC converter. The LT4271-LT4290 solution shown in Figure 2 eliminates these components.


design ideas

opto-couplers. Intra-IC communication

including port management, reset and

fast port shutdown are encoded in a

protocol designed to minimize radiated

energy and provide 1500V of isolation.

ADVANCED FOURTH GENERATION FEATURES

Linear’s PSE family incorporates a wealth

of PoE experience and expertise backed

by well over 100 million shipped ports.

This latest PSE generation adds features

to a proven, field-tested product line.

New features include field-upgradable

firmware, future-proofing platforms that

incorporate the LTC4290/LTC4271. Also

new is optional 1-second current averag-

ing, which simplifies host power manage-

ment. The highest grade LTC4290A analog

controller enables delivered PD power

of up to 90W using the new LTPoE++™

physical classification scheme.

As with previous generations, a key benefit

of the LTC4290/LTC4271 chipset archi-

tecture is the lowest-in-industry power

dissipation, making thermal design signifi-

cantly easier than designing with PSEs that

integrate more fragile and higher RDS(ON)

MOSFETs. System designers will appreciate

the robustness provided by 80V-tolerant

port pins. PD discovery is accomplished

using a proprietary dual-mode, 4-point

SYSTEM ISOLATION REQUIREMENTS

The PoE specification clearly lays out

isolation requirements, guaranteeing

ground loops are broken, maintaining

Ethernet data integrity and minimiz-

ing noise in the PD application circuit.

Traditional PSE isolation architectures

isolate the digital interface and power

at the host-to-PSE controller interface.

Digital isolation elements such as opto-

couplers are inherently expensive and

unreliable. ICs capable of performing

the isolation function are cost-prohib-

itive or do not support fast I2C transfer

rates. In addition, isolated DC/DC con-

verters needed to power the PSE logic

increase board space and system cost.

ISOLATION MADE EASY

The LTC4290/LTC4271 chipset takes a dif-

ferent approach to PSE isolation (Figure 2)

by moving all digital functions to the

host side of the isolation barrier. This

significantly reduces the cost and complex-

ity of required components. There is no

longer the need for a separate, isolated

DC/DC power supply; the LTC4271 digital

controller can use the host’s logic supply.

The LTC4271 controls the LTC4290 using

a transformer-isolated communication

scheme. An inexpensive and ubiquitous

Ethernet transformer pair replaces six

detection mechanism that ensures

immunity from false PD detection.

Advanced power management includes

prioritized fast shutdown, 12-bit per-port

voltage and current read back, 8-bit pro-

grammable current limits and 7-bit pro-

grammable overload current thresholds.

A 1MHz I2C interface allows a host

controller to digitally configure the

IC or query port readings. “C” librar-

ies are available to reduce engineering

costs and improve time to market.

CONCLUSION

The LTC4290/LTC4271 builds on

an established, robust lineup of

Linear PSE solutions by slash-

ing BOM costs while providing an

overall best-in-field solution. n

1500V ISOLATION

PSE PD

PDCONTROLLER

PHY

LT4271 LT4290

HOST

PHY

ISOLATEDDC/DC

CONVERTER

Figure 2. In contrast to the traditional scheme shown in Figure 1, a cleaner PSE architecture incorporates the LTC4290/LTC4271 chipset, achieving isolation without any opto-isolators and eliminatinating the need for a dedicated isolated DC/DC converter.


Product Briefs

NANO-CURRENT HIGH VOLTAGE MONITOR

The LTC2960 is a nano-current high volt-

age monitor that provides supervisory

reset generation and undervoltage or

overvoltage detection. Low quiescent

current (0.85µA) and a wide operat-

ing voltage range of 2.5V to 36V make

the LTC2960 useful in multicell battery

applications. Status indicators RST and

OUT are available with 36V open-drains

or low voltage active pull-ups.

External resistive dividers configure

monitor thresholds for each of the two

comparator inputs. The LTC2960 moni-

tors the ADJ input and pulls RST output

low when the voltage at the compara-

tor input drops below the comparator

threshold. RST remains low until the

ADJ input rises 2.5% above the threshold.

A reset timeout period delays the return

of the RST output to a high state to allow

voltage settling, initialization time and/

or a microprocessor reset function. An

additional comparator with inverting or

noninverting input includes 5% hyster-

esis and is indicated on the OUT pin.

A manual reset (MR) input enables exter-

nal activation of the RST output. Other

options include a selectable 15ms or

200ms reset timeout periods. A logic sup-

ply pin, DVCC, provides a power input for

the active pull-up circuits. The LTC2960 is

available in 8-lead 2mm × 2mm DFN and

TSOT-23 packages. Electrical specifications

are guaranteed from –45ºC to 125ºC.

MULTIPHASE STEP-UP DC/DC PROVIDES 10V GATE DRIVE, RIDES THROUGH COLD CRANK

The LTC3862-2 is a high power multiphase

current mode step-up DC/DC controller.

Like its predecessors, the LTC3862

and LTC3862-1, the LTC3862-2 uses

a constant frequency, peak current

mode architecture with two channels

operating 180° out of phase. It retains

popular features, including adjustable

slope compensation gain, max duty

cycle and leading edge blanking,

programmable frequency with a external

resistor (75kHz to 500kHz) or SYNC to

an external clock with a phase-lockable

fixed frequency of 50kHz to 650kHz.

The PHASEMODE control pin allows for

2-, 3-, 4-, 6-, or 12-phase operation.

Like the LTC3861-1, the LTC3862-2’s

internal LDO regulates to 10V, optimizing

gate drive for most automotive and

industrial grade power MOSFETs. But

unlike the LTC3861-1, the LTC3862-2’s

undervoltage lockout (UVLO) falling

threshold is reduced to 4V from the

original 7V. UVLO shuts off the circuit

when there is not enough gate drive.

Lowering it provides compatibility with

the most efficient 10V gate drive MOSFETs,

while allowing the part to regulate

even when the input voltage dips below

10V (as when an engine is turned on).

The LTC3862-2 also has improved

current sense matching, channel-to-

channel and chip-to-chip. This allows

thermal dissipation to be shared

more evenly between phases.

FULLY DIFFERENTIAL AMPLIFIER DRIVES 18-BIT ADCs & CONSUMES ONLY 5mW

Linear Technology announces the LTC6362,

a low power fully differential amplifier

that can drive high precision 16- and

18-bit SAR ADCs at only 1mA supply cur-

rent. With 200µV max input offset volt-

age and 3.9nV/√Hz input-referred noise,

it is well suited for precision industrial

and data acquisition applications.

The LTC6362 has an output common-

mode pin with a 0.5V to 4.5V range, and

18-bit settling time of 550ns with an

8VP–P output step, making it ideal for

driving ADCs such as the LTC2379-18

in multiplexed input and control loop

applications. This 18-bit SAR ADC features

digital gain compression, which sets its

full scale input range at 10% to 90% of

the reference voltage. Together with the

rail-to-rail output stage of the LTC6362,

this feature eliminates the need for a

negative supply rail, simplifying the circuit

and minimizing power consumption.

The flexible architecture of the LTC6362

can convert single-ended DC-coupled,

ground-referenced signals to differential,

or DC level shift differential input signals.

The low input bias current, low offset

voltage and rail-to-rail inputs of the

LTC6362 enable its use in a high imped-

ance configuration to interface directly

to sensors early in the signal chain.

The LTC6362 is available in MSOP-8

and 3mm × 3mm DFN packages, with

fully guaranteed specifications over

the 0°C to 70°C, –40°C to 85°C and

–40°C to 125°C temperature ranges.


product briefs

60V SYNCHRONOUS BUCK-BOOST LED DRIVER DELIVERS OVER 100W OF LED POWER

The LT3791 is a synchronous buck-boost

DC/DC LED driver and voltage controller,

which can deliver over 100W of LED power.

Its 4.7V to 60V input voltage range makes

it ideal for a wide variety of applica-

tions, including automotive, industrial

and architectural lighting. Similarly, its

output voltage can be set from 0V to 60V,

enabling the LT3791 to drive a wide range

of LEDs in a single string. Its internal

4-switch buck-boost controller operates

from input voltages above, below or equal

to the output voltage, ideal for applica-

tions such as automotive, where the input

voltage can vary dramatically during stop/

start, cold crank and load dump scenarios.

Transitions between buck, pass-through

and boost operating modes are seam-

less, offering a well regulated output even

with wide variations of supply voltage.

The LT3791’s unique design utilizes three

control loops to monitor input current,

LED current and output voltage to deliver

optimal performance and reliability.

The LT3791 uses four external switching

MOSFETs and delivers from 5W to over

100W of continuous LED power with effi-

ciencies up to 98.5%. LED current accuracy

of +6% ensures constant lighting while

±2% output voltage accuracy enables the

converter to operate as a constant voltage

source. The LT3791 utilizes either ana-

log or PWM dimming as required by the

application. Furthermore, its switching

frequency can be programmed between

200kHz and 700kHz or synchronized to

an external clock. Additional features

include output disconnect, input and

output current monitors, open and shorted

LED detection and integrated fault protec-

tion. The LT3791EFE is available in 38-lead

thermally enhanced TSSOP package.

30MHz TO 1.4GHZ WIDEBAND I/Q DEMODULATOR WITH IIP2 OPTIMIZATION & DC OFFSET CANCELLATION IMPROVES ZERO-IF RECEIVER PERFORMANCE

The LTC5584 is an ultrawide bandwidth

direct conversion I/Q demodulator with

outstanding linearity of 31dBm IIP3 and

70dBm IIP2. The device offers best-in-class

demodulation bandwidth of over 530MHz,

supporting the latest generation of

LTE multimode, LTE Advanced receivers, as

well as digital predistortion (DPD) receiv-

ers. The I/Q demodulator operates over

a wide frequency range from 30MHz to

1.4GHz, covering a broad range of VHF and

UHF radios and the 450MHz/700MHz

LTE frequency bands. Unique to the

LTC5584 are two built-in calibration

features. One is advanced circuitry that

enables the system designer to optimize

the receiver’s IIP2 performance, increas-

ing from a nominal 70dBm to an unprec-

edented 80dBm or higher. The other is

on-chip circuitry to null out the DC offset

voltages at the I and Q outputs. Combined

with a 9.9dB noise figure, these features

enhance the dynamic range perfor-

mance in receivers. Moreover, the device

exacts P1dB of 12.6dBm, along with its

13.6dB noise figure under a 0dBm in-band

blocker, ensuring robust receiver perfor-

mance in the presence of interference.

To enhance its flexibility for use in low

IF receiver applications, the LTC5584

exhibits very low I/Q amplitude and phase

mismatch. The amplitude mismatch is

typically 0.02dB, while the phase error

is typically 0.25 degree, both specified

at 450MHz. This combination produces

receiver image rejection of 52dB.

With its wide bandwidth capabil-

ity, the LTC5584 is ideal for multimode

LTE and CDMA DPD receivers as well as

other wideband receiver applications.

Particularly suited for DPD, these lat-

est generation base stations are pushing

demodulation bandwidth of over 300MHz.

The LTC5584 exceeds these bandwidth

requirements while delivering better than

±0.5dB conversion gain flatness. Beyond

wireless infrastructure applications, the

LTC5584 is ideal for military receivers,

broadband communications, point-to-

point microwave data links, image-reject

receivers and long-range RFID readers.

The LTC5584 is offered in a 24-lead

4mm × 4mm QFN package. The device

is specified for case operating tempera-

ture from –40°C to 105°C. Powered from

a single 5V supply, the LTC5584 draws

a total supply current of 200mA. The

device provides a digital input to enable

or disable the chip. When disabled, the

IC draws 11µA of leakage current typical.

The demodulator’s fast turn-on time of

200ns and turn-off time of 800ns enables

it to be used in burst-mode receivers. n

The LTC2960 is a nano-current high voltage monitor that provides supervisory reset generation and undervoltage or overvoltage detection. Low quiescent current (0.85μA) and a wide operating voltage range of 2.5V to 36V make the LTC2960 useful in multicell battery applications.

DEVICE OPTION OUTPUT TYPE INPUTS RESET TIMEOUT PERIOD

LTC2960-1 36V Open Drain ADJ/IN+ 15ms/200ms

LTC2960-2 36V Open Drain ADJ/IN- 15ms/200ms

LTC2960-3 Active Pull-up ADJ/IN+ 200ms

LTC2960-4 Active Pull-up ADJ/IN- 200ms

http://www.linear.com/product/LTC5584

highlights from circuits.linear.com

Linear Technology Corporation 1630 McCarthy Boulevard, Milpitas, CA 95035 (408) 432-1900 www.linear.com Cert no. SW-COC-001530

L, LT, LTC, LTM, Linear Technology, the Linear logo, LTspice, Burst Mode, Dust Networks, PolyPhase and µModule are registered trademarks, and Eterna, Hot Swap, LTpowerPlay, LTPoE++ and SmartMesh are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. © 2012 Linear Technology Corporation/Printed in U.S.A./57K

–3.3V NEGATIVE CONVERTER WITH 1A OUTPUT CURRENT LIMITThe LT8611 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 2.5μA of quiescent current. Top and bottom power switches are included with all necessary circuitry to minimize the need for external components. The built-in current sense amplifier with monitor and control pins allows accurate input or output current regulation and limiting. Low ripple Burst Mode® operation enables high efficiency down to very low output currents while keeping the output ripple below 10mVP–P.circuits.linear.com/585


2A, 4-CELL LI-ION BATTERY CHARGER WITH C/10 TERMINATIONThe LTM8062/LTM8062A are complete 32V VIN, 2A μModule power tracking battery chargers. The LTM8062/ LTM8062A provide a constant-current/constant-voltage charge characteristic, a 2A maximum charge current, and employ a 3.3V float voltage feedback reference, so any desired battery float voltage up to 14.4V for the LTM8062 and up to 18.8V for the LTM8062A can be programmed with a resistor divider.circuits.linear.com/584


4.3V TO 42V INPUT, 3.3V, 5A OUTPUT STEP-DOWN CONVERTERThe LT3976 is an adjustable frequency monolithic buck switching regulator that accepts a wide input voltage range up to 40V. Low quiescent current design consumes only 3.3μA of supply current while regulating with no load. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping the output ripple below 15mV in a typical application.circuits.linear.com/583


BSTVIN

EN/UV

SYNC

IMON

60.4k

0.1µF

ICTRL

INTVCC

TR/SS

RT

SW

LT8611

GND

ISP

ISNBIAS

PG

FB

0.1µF

1µF

VOUT–3.3V1A

10pF

47µF

4.7µF

VIN3.8V TO 38V

1µF

0.1µF

4.7µH

1M

0.05Ω412k60.4k

f = 700kHz

PGND

4.7µF

LTM8062A

GND

VINA

VIN

VINREG

RUN

TMR

NTC

VIN22V TO 32VDC

BAT

CHRG

FAULT

ADJ

BIAS

4.7µF1.24M

312k

EXTERNAL 3.3V

4-CELLLi-Ion(4 × 4.1V)BATTERYPACK

(OPTIONALELECTROLYTICCAPACITOR)

+

VINEN BOOSTOFF ON

VIN4.3V TO 42V

PG0.47µF

470pF

PDS540

47µF2

10nF

10µF

576k

f = 400kHz

130k

VOUT3.3V5A

3.3µH

LT3976

SS

RT

SW

OUT

FBSYNC GND

1M

2Ω

10pF

http://circuits.linear.com

http://www.linear.com










Documents

LT Journal of Analog Innovation V22N3